diff --git a/CHANGELOG.md b/CHANGELOG.md
index 47e6f06..d53b35f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- NewTask function now takes array of bytes as payload.
+- Task `Type` and `Payload` should be accessed by a method call.
 - Requires redis v4.0+ for multiple field/value pair support
 - Renamed pending key (TODO: need migration script
 
diff --git a/README.md b/README.md
index cbc5882..1f7c064 100644
--- a/README.md
+++ b/README.md
@@ -12,8 +12,8 @@ Asynq is a Go library for queueing tasks and processing them asynchronously with
 
 Highlevel overview of how Asynq works:
 
-- Client puts task on a queue
-- Server pulls task off queues and starts a worker goroutine for each task
+- Client puts tasks on a queue
+- Server pulls tasks off queues and starts a worker goroutine for each task
 - Tasks are processed concurrently by multiple workers
 
 Task queues are used as a mechanism to distribute work across multiple machines. A system can consist of multiple worker servers and brokers, giving way to high availability and horizontal scaling.
@@ -77,19 +77,36 @@ const (
     TypeImageResize     = "image:resize"
 )
 
+type EmailDeliveryPayload struct {
+    UserID     int
+    TemplateID string
+}
+
+type ImageResizePayload struct {
+    SourceURL string
+}
+
 //----------------------------------------------
 // Write a function NewXXXTask to create a task.
 // A task consists of a type and a payload.
 //----------------------------------------------
 
-func NewEmailDeliveryTask(userID int, tmplID string) *asynq.Task {
-    payload := map[string]interface{}{"user_id": userID, "template_id": tmplID}
-    return asynq.NewTask(TypeEmailDelivery, payload)
+func NewEmailDeliveryTask(userID int, tmplID string) (*asynq.Task, error) {
+    payload := EmailDeliveryPayload{UserID: userID, TemplateID: templID}
+    bytes, err := json.Marshal(payload)
+    if err != nil {
+        return nil, err
+    }
+    return asynq.NewTask(TypeEmailDelivery, bytes), nil
 }
 
-func NewImageResizeTask(src string) *asynq.Task {
-    payload := map[string]interface{}{"src": src}
-    return asynq.NewTask(TypeImageResize, payload)
+func NewImageResizeTask(src string) (*asynq.Task, error) {
+    payload := ImageResizePayload{SourceURL: src}
+    bytes, err := json.Marshal(payload)
+    if err != nil {
+        return nil, err
+    }
+    return asynq.NewTask(TypeImageResize, bytes), nil
 }
 
 //---------------------------------------------------------------
@@ -101,15 +118,11 @@ func NewImageResizeTask(src string) *asynq.Task {
 //---------------------------------------------------------------
 
 func HandleEmailDeliveryTask(ctx context.Context, t *asynq.Task) error {
-    userID, err := t.Payload.GetInt("user_id")
-    if err != nil {
-        return err
+    var p EmailDeliveryPayload
+    if err := json.Unmarshal(t.Payload(), &p); err != nil {
+        return fmt.Errorf("json.Unmarshal failed: %v: %w", err, asynq.SkipRetry)
     }
-    tmplID, err := t.Payload.GetString("template_id")
-    if err != nil {
-        return err
-    }
-    fmt.Printf("Send Email to User: user_id = %d, template_id = %s\n", userID, tmplID)
+    log.Printf("Sending Email to User: user_id = %d, template_id = %s\n", p.UserID, p.TemplateID)
     // Email delivery code ...
     return nil
 }
@@ -120,11 +133,11 @@ type ImageProcessor struct {
 }
 
 func (p *ImageProcessor) ProcessTask(ctx context.Context, t *asynq.Task) error {
-    src, err := t.Payload.GetString("src")
-    if err != nil {
-        return err
+    var p ImageResizePayload
+    if err := json.Unmarshal(t.Payload(), &p); err != nil {
+        return fmt.Errorf("json.Unmarshal failed: %v: %w", err, asynq.SkipRetry)
     }
-    fmt.Printf("Resize image: src = %s\n", src)
+    log.Printf("Resizing image: src = %s\n", p.SourceURL)
     // Image resizing code ...
     return nil
 }
@@ -160,10 +173,13 @@ func main() {
     //            Use (*Client).Enqueue method.
     // ------------------------------------------------------
 
-    t := tasks.NewEmailDeliveryTask(42, "some:template:id")
+    t, err := tasks.NewEmailDeliveryTask(42, "some:template:id")
+    if err != nil {
+        log.Fatalf("could not create task: %v", err)
+    }
     res, err := c.Enqueue(t)
     if err != nil {
-        log.Fatal("could not enqueue task: %v", err)
+        log.Fatalf("could not enqueue task: %v", err)
     }
     fmt.Printf("Enqueued Result: %+v\n", res)
 
@@ -173,10 +189,9 @@ func main() {
     //            Use ProcessIn or ProcessAt option.
     // ------------------------------------------------------------
 
-    t = tasks.NewEmailDeliveryTask(42, "other:template:id")
     res, err = c.Enqueue(t, asynq.ProcessIn(24*time.Hour))
     if err != nil {
-        log.Fatal("could not schedule task: %v", err)
+        log.Fatalf("could not schedule task: %v", err)
     }
     fmt.Printf("Enqueued Result: %+v\n", res)
 
@@ -188,19 +203,21 @@ func main() {
 
     c.SetDefaultOptions(tasks.TypeImageResize, asynq.MaxRetry(10), asynq.Timeout(3*time.Minute))
 
-    t = tasks.NewImageResizeTask("some/blobstore/path")
+    t, err = tasks.NewImageResizeTask("https://example.com/myassets/image.jpg")
+    if err != nil {
+        log.Fatalf("could not create task: %v", err)
+    }
     res, err = c.Enqueue(t)
     if err != nil {
-        log.Fatal("could not enqueue task: %v", err)
+        log.Fatalf("could not enqueue task: %v", err)
     }
     fmt.Printf("Enqueued Result: %+v\n", res)
 
     // ---------------------------------------------------------------------------
     // Example 4: Pass options to tune task processing behavior at enqueue time.
-    //            Options passed at enqueue time override default ones, if any.
+    //            Options passed at enqueue time override default ones.
     // ---------------------------------------------------------------------------
 
-    t = tasks.NewImageResizeTask("some/blobstore/path")
     res, err = c.Enqueue(t, asynq.Queue("critical"), asynq.Timeout(30*time.Second))
     if err != nil {
         log.Fatal("could not enqueue task: %v", err)
diff --git a/asynq.go b/asynq.go
index 39e16cb..6a7a65f 100644
--- a/asynq.go
+++ b/asynq.go
@@ -17,20 +17,21 @@ import (
 
 // Task represents a unit of work to be performed.
 type Task struct {
-	// Type indicates the type of task to be performed.
-	Type string
+	// typename indicates the type of task to be performed.
+	typename string
 
-	// Payload holds data needed to perform the task.
-	Payload Payload
+	// payload holds data needed to perform the task.
+	payload []byte
 }
 
+func (t *Task) Type() string    { return t.typename }
+func (t *Task) Payload() []byte { return t.payload }
+
 // NewTask returns a new Task given a type name and payload data.
-//
-// The payload values must be serializable.
-func NewTask(typename string, payload map[string]interface{}) *Task {
+func NewTask(typename string, payload []byte) *Task {
 	return &Task{
-		Type:    typename,
-		Payload: Payload{payload},
+		typename: typename,
+		payload:  payload,
 	}
 }
 
diff --git a/asynq_test.go b/asynq_test.go
index 2ca46d4..c763a05 100644
--- a/asynq_test.go
+++ b/asynq_test.go
@@ -85,7 +85,7 @@ func getRedisConnOpt(tb testing.TB) RedisConnOpt {
 var sortTaskOpt = cmp.Transformer("SortMsg", func(in []*Task) []*Task {
 	out := append([]*Task(nil), in...) // Copy input to avoid mutating it
 	sort.Slice(out, func(i, j int) bool {
-		return out[i].Type < out[j].Type
+		return out[i].Type() < out[j].Type()
 	})
 	return out
 })
diff --git a/benchmark_test.go b/benchmark_test.go
index a4d7db2..b98ea34 100644
--- a/benchmark_test.go
+++ b/benchmark_test.go
@@ -6,12 +6,24 @@ package asynq
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"sync"
 	"testing"
 	"time"
+
+	h "github.com/hibiken/asynq/internal/asynqtest"
 )
 
+// Creates a new task of type "task<n>" with payload {"data": n}.
+func makeTask(n int) *Task {
+	b, err := json.Marshal(map[string]int{"data": n})
+	if err != nil {
+		panic(err)
+	}
+	return NewTask(fmt.Sprintf("task%d", n), b)
+}
+
 // Simple E2E Benchmark testing with no scheduled tasks and retries.
 func BenchmarkEndToEndSimple(b *testing.B) {
 	const count = 100000
@@ -29,8 +41,7 @@ func BenchmarkEndToEndSimple(b *testing.B) {
 		})
 		// Create a bunch of tasks
 		for i := 0; i < count; i++ {
-			t := NewTask(fmt.Sprintf("task%d", i), map[string]interface{}{"data": i})
-			if _, err := client.Enqueue(t); err != nil {
+			if _, err := client.Enqueue(makeTask(i)); err != nil {
 				b.Fatalf("could not enqueue a task: %v", err)
 			}
 		}
@@ -70,14 +81,12 @@ func BenchmarkEndToEnd(b *testing.B) {
 		})
 		// Create a bunch of tasks
 		for i := 0; i < count; i++ {
-			t := NewTask(fmt.Sprintf("task%d", i), map[string]interface{}{"data": i})
-			if _, err := client.Enqueue(t); err != nil {
+			if _, err := client.Enqueue(makeTask(i)); err != nil {
 				b.Fatalf("could not enqueue a task: %v", err)
 			}
 		}
 		for i := 0; i < count; i++ {
-			t := NewTask(fmt.Sprintf("scheduled%d", i), map[string]interface{}{"data": i})
-			if _, err := client.Enqueue(t, ProcessIn(1*time.Second)); err != nil {
+			if _, err := client.Enqueue(makeTask(i), ProcessIn(1*time.Second)); err != nil {
 				b.Fatalf("could not enqueue a task: %v", err)
 			}
 		}
@@ -86,13 +95,18 @@ func BenchmarkEndToEnd(b *testing.B) {
 		var wg sync.WaitGroup
 		wg.Add(count * 2)
 		handler := func(ctx context.Context, t *Task) error {
-			n, err := t.Payload.GetInt("data")
-			if err != nil {
+			var p map[string]int
+			if err := json.Unmarshal(t.Payload(), &p); err != nil {
 				b.Logf("internal error: %v", err)
 			}
+			n, ok := p["data"]
+			if !ok {
+				n = 1
+				b.Logf("internal error: could not get data from payload")
+			}
 			retried, ok := GetRetryCount(ctx)
 			if !ok {
-				b.Logf("internal error: %v", err)
+				b.Logf("internal error: could not get retry count from context")
 			}
 			// Fail 1% of tasks for the first attempt.
 			if retried == 0 && n%100 == 0 {
@@ -136,20 +150,17 @@ func BenchmarkEndToEndMultipleQueues(b *testing.B) {
 		})
 		// Create a bunch of tasks
 		for i := 0; i < highCount; i++ {
-			t := NewTask(fmt.Sprintf("task%d", i), map[string]interface{}{"data": i})
-			if _, err := client.Enqueue(t, Queue("high")); err != nil {
+			if _, err := client.Enqueue(makeTask(i), Queue("high")); err != nil {
 				b.Fatalf("could not enqueue a task: %v", err)
 			}
 		}
 		for i := 0; i < defaultCount; i++ {
-			t := NewTask(fmt.Sprintf("task%d", i), map[string]interface{}{"data": i})
-			if _, err := client.Enqueue(t); err != nil {
+			if _, err := client.Enqueue(makeTask(i)); err != nil {
 				b.Fatalf("could not enqueue a task: %v", err)
 			}
 		}
 		for i := 0; i < lowCount; i++ {
-			t := NewTask(fmt.Sprintf("task%d", i), map[string]interface{}{"data": i})
-			if _, err := client.Enqueue(t, Queue("low")); err != nil {
+			if _, err := client.Enqueue(makeTask(i), Queue("low")); err != nil {
 				b.Fatalf("could not enqueue a task: %v", err)
 			}
 		}
@@ -190,15 +201,13 @@ func BenchmarkClientWhileServerRunning(b *testing.B) {
 		})
 		// Enqueue 10,000 tasks.
 		for i := 0; i < count; i++ {
-			t := NewTask(fmt.Sprintf("task%d", i), map[string]interface{}{"data": i})
-			if _, err := client.Enqueue(t); err != nil {
+			if _, err := client.Enqueue(makeTask(i)); err != nil {
 				b.Fatalf("could not enqueue a task: %v", err)
 			}
 		}
 		// Schedule 10,000 tasks.
 		for i := 0; i < count; i++ {
-			t := NewTask(fmt.Sprintf("scheduled%d", i), map[string]interface{}{"data": i})
-			if _, err := client.Enqueue(t, ProcessIn(1*time.Second)); err != nil {
+			if _, err := client.Enqueue(makeTask(i), ProcessIn(1*time.Second)); err != nil {
 				b.Fatalf("could not enqueue a task: %v", err)
 			}
 		}
@@ -213,7 +222,7 @@ func BenchmarkClientWhileServerRunning(b *testing.B) {
 		b.Log("Starting enqueueing")
 		enqueued := 0
 		for enqueued < 100000 {
-			t := NewTask(fmt.Sprintf("enqueued%d", enqueued), map[string]interface{}{"data": enqueued})
+			t := NewTask(fmt.Sprintf("enqueued%d", enqueued), h.JSON(map[string]interface{}{"data": enqueued}))
 			if _, err := client.Enqueue(t); err != nil {
 				b.Logf("could not enqueue task %d: %v", enqueued, err)
 				continue
diff --git a/client.go b/client.go
index 9402099..dc1841c 100644
--- a/client.go
+++ b/client.go
@@ -176,7 +176,6 @@ func (d processInOption) String() string     { return fmt.Sprintf("ProcessIn(%v)
 func (d processInOption) Type() OptionType   { return ProcessInOpt }
 func (d processInOption) Value() interface{} { return time.Duration(d) }
 
-
 // ErrDuplicateTask indicates that the given task could not be enqueued since it's a duplicate of another task.
 //
 // ErrDuplicateTask error only applies to tasks enqueued with a Unique option.
@@ -305,7 +304,7 @@ func (c *Client) Close() error {
 // If no ProcessAt or ProcessIn options are passed, the task will be processed immediately.
 func (c *Client) Enqueue(task *Task, opts ...Option) (*Result, error) {
 	c.mu.Lock()
-	if defaults, ok := c.opts[task.Type]; ok {
+	if defaults, ok := c.opts[task.Type()]; ok {
 		opts = append(defaults, opts...)
 	}
 	c.mu.Unlock()
@@ -327,12 +326,12 @@ func (c *Client) Enqueue(task *Task, opts ...Option) (*Result, error) {
 	}
 	var uniqueKey string
 	if opt.uniqueTTL > 0 {
-		uniqueKey = base.UniqueKey(opt.queue, task.Type, task.Payload.data)
+		uniqueKey = base.UniqueKey(opt.queue, task.Type(), task.Payload())
 	}
 	msg := &base.TaskMessage{
 		ID:        uuid.New(),
-		Type:      task.Type,
-		Payload:   task.Payload.data,
+		Type:      task.Type(),
+		Payload:   task.Payload(),
 		Queue:     opt.queue,
 		Retry:     opt.retry,
 		Deadline:  deadline.Unix(),
diff --git a/client_test.go b/client_test.go
index c3207ef..cc1dacc 100644
--- a/client_test.go
+++ b/client_test.go
@@ -20,7 +20,7 @@ func TestClientEnqueueWithProcessAtOption(t *testing.T) {
 	client := NewClient(getRedisConnOpt(t))
 	defer client.Close()
 
-	task := NewTask("send_email", map[string]interface{}{"to": "customer@gmail.com", "from": "merchant@example.com"})
+	task := NewTask("send_email", h.JSON(map[string]interface{}{"to": "customer@gmail.com", "from": "merchant@example.com"}))
 
 	var (
 		now          = time.Now()
@@ -52,8 +52,8 @@ func TestClientEnqueueWithProcessAtOption(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"default": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    defaultMaxRetry,
 						Queue:    "default",
 						Timeout:  int64(defaultTimeout.Seconds()),
@@ -85,8 +85,8 @@ func TestClientEnqueueWithProcessAtOption(t *testing.T) {
 				"default": {
 					{
 						Message: &base.TaskMessage{
-							Type:     task.Type,
-							Payload:  task.Payload.data,
+							Type:     task.Type(),
+							Payload:  task.Payload(),
 							Retry:    defaultMaxRetry,
 							Queue:    "default",
 							Timeout:  int64(defaultTimeout.Seconds()),
@@ -137,7 +137,7 @@ func TestClientEnqueue(t *testing.T) {
 	client := NewClient(getRedisConnOpt(t))
 	defer client.Close()
 
-	task := NewTask("send_email", map[string]interface{}{"to": "customer@gmail.com", "from": "merchant@example.com"})
+	task := NewTask("send_email", h.JSON(map[string]interface{}{"to": "customer@gmail.com", "from": "merchant@example.com"}))
 	now := time.Now()
 
 	tests := []struct {
@@ -163,8 +163,8 @@ func TestClientEnqueue(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"default": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    3,
 						Queue:    "default",
 						Timeout:  int64(defaultTimeout.Seconds()),
@@ -189,8 +189,8 @@ func TestClientEnqueue(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"default": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    0, // Retry count should be set to zero
 						Queue:    "default",
 						Timeout:  int64(defaultTimeout.Seconds()),
@@ -216,8 +216,8 @@ func TestClientEnqueue(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"default": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    10, // Last option takes precedence
 						Queue:    "default",
 						Timeout:  int64(defaultTimeout.Seconds()),
@@ -242,8 +242,8 @@ func TestClientEnqueue(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"custom": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    defaultMaxRetry,
 						Queue:    "custom",
 						Timeout:  int64(defaultTimeout.Seconds()),
@@ -268,8 +268,8 @@ func TestClientEnqueue(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"high": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    defaultMaxRetry,
 						Queue:    "high",
 						Timeout:  int64(defaultTimeout.Seconds()),
@@ -294,8 +294,8 @@ func TestClientEnqueue(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"default": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    defaultMaxRetry,
 						Queue:    "default",
 						Timeout:  20,
@@ -320,8 +320,8 @@ func TestClientEnqueue(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"default": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    defaultMaxRetry,
 						Queue:    "default",
 						Timeout:  int64(noTimeout.Seconds()),
@@ -347,8 +347,8 @@ func TestClientEnqueue(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"default": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    defaultMaxRetry,
 						Queue:    "default",
 						Timeout:  20,
@@ -390,7 +390,7 @@ func TestClientEnqueueWithProcessInOption(t *testing.T) {
 	client := NewClient(getRedisConnOpt(t))
 	defer client.Close()
 
-	task := NewTask("send_email", map[string]interface{}{"to": "customer@gmail.com", "from": "merchant@example.com"})
+	task := NewTask("send_email", h.JSON(map[string]interface{}{"to": "customer@gmail.com", "from": "merchant@example.com"}))
 	now := time.Now()
 
 	tests := []struct {
@@ -421,8 +421,8 @@ func TestClientEnqueueWithProcessInOption(t *testing.T) {
 				"default": {
 					{
 						Message: &base.TaskMessage{
-							Type:     task.Type,
-							Payload:  task.Payload.data,
+							Type:     task.Type(),
+							Payload:  task.Payload(),
 							Retry:    defaultMaxRetry,
 							Queue:    "default",
 							Timeout:  int64(defaultTimeout.Seconds()),
@@ -448,8 +448,8 @@ func TestClientEnqueueWithProcessInOption(t *testing.T) {
 			wantPending: map[string][]*base.TaskMessage{
 				"default": {
 					{
-						Type:     task.Type,
-						Payload:  task.Payload.data,
+						Type:     task.Type(),
+						Payload:  task.Payload(),
 						Retry:    defaultMaxRetry,
 						Queue:    "default",
 						Timeout:  int64(defaultTimeout.Seconds()),
@@ -501,7 +501,7 @@ func TestClientEnqueueError(t *testing.T) {
 	client := NewClient(getRedisConnOpt(t))
 	defer client.Close()
 
-	task := NewTask("send_email", map[string]interface{}{"to": "customer@gmail.com", "from": "merchant@example.com"})
+	task := NewTask("send_email", h.JSON(map[string]interface{}{"to": "customer@gmail.com", "from": "merchant@example.com"}))
 
 	tests := []struct {
 		desc string
@@ -613,7 +613,7 @@ func TestClientDefaultOptions(t *testing.T) {
 		h.FlushDB(t, r)
 		c := NewClient(getRedisConnOpt(t))
 		defer c.Close()
-		c.SetDefaultOptions(tc.task.Type, tc.defaultOpts...)
+		c.SetDefaultOptions(tc.task.Type(), tc.defaultOpts...)
 		gotRes, err := c.Enqueue(tc.task, tc.opts...)
 		if err != nil {
 			t.Fatal(err)
@@ -650,7 +650,7 @@ func TestClientEnqueueUnique(t *testing.T) {
 		ttl  time.Duration
 	}{
 		{
-			NewTask("email", map[string]interface{}{"user_id": 123}),
+			NewTask("email", h.JSON(map[string]interface{}{"user_id": 123})),
 			time.Hour,
 		},
 	}
@@ -664,7 +664,7 @@ func TestClientEnqueueUnique(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		gotTTL := r.TTL(base.UniqueKey(base.DefaultQueueName, tc.task.Type, tc.task.Payload.data)).Val()
+		gotTTL := r.TTL(base.UniqueKey(base.DefaultQueueName, tc.task.Type(), tc.task.Payload())).Val()
 		if !cmp.Equal(tc.ttl.Seconds(), gotTTL.Seconds(), cmpopts.EquateApprox(0, 1)) {
 			t.Errorf("TTL = %v, want %v", gotTTL, tc.ttl)
 			continue
@@ -709,7 +709,7 @@ func TestClientEnqueueUniqueWithProcessInOption(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		gotTTL := r.TTL(base.UniqueKey(base.DefaultQueueName, tc.task.Type, tc.task.Payload.data)).Val()
+		gotTTL := r.TTL(base.UniqueKey(base.DefaultQueueName, tc.task.Type(), tc.task.Payload())).Val()
 		wantTTL := time.Duration(tc.ttl.Seconds()+tc.d.Seconds()) * time.Second
 		if !cmp.Equal(wantTTL.Seconds(), gotTTL.Seconds(), cmpopts.EquateApprox(0, 1)) {
 			t.Errorf("TTL = %v, want %v", gotTTL, wantTTL)
@@ -755,7 +755,7 @@ func TestClientEnqueueUniqueWithProcessAtOption(t *testing.T) {
 			t.Fatal(err)
 		}
 
-		gotTTL := r.TTL(base.UniqueKey(base.DefaultQueueName, tc.task.Type, tc.task.Payload.data)).Val()
+		gotTTL := r.TTL(base.UniqueKey(base.DefaultQueueName, tc.task.Type(), tc.task.Payload())).Val()
 		wantTTL := tc.at.Add(tc.ttl).Sub(time.Now())
 		if !cmp.Equal(wantTTL.Seconds(), gotTTL.Seconds(), cmpopts.EquateApprox(0, 1)) {
 			t.Errorf("TTL = %v, want %v", gotTTL, wantTTL)
@@ -774,4 +774,3 @@ func TestClientEnqueueUniqueWithProcessAtOption(t *testing.T) {
 		}
 	}
 }
-
diff --git a/doc.go b/doc.go
index edd3865..06ede25 100644
--- a/doc.go
+++ b/doc.go
@@ -11,7 +11,7 @@ specify the connection using one of RedisConnOpt types.
     redisConnOpt = asynq.RedisClientOpt{
         Addr:     "127.0.0.1:6379",
         Password: "xxxxx",
-        DB:       3,
+        DB:       2,
     }
 
 The Client is used to enqueue a task.
@@ -20,12 +20,16 @@ The Client is used to enqueue a task.
     client := asynq.NewClient(redisConnOpt)
 
     // Task is created with two parameters: its type and payload.
-    t := asynq.NewTask(
-        "send_email",
-        map[string]interface{}{"user_id": 42})
+    // Payload data is simply an array of bytes. It can be encoded in JSON, Protocol Buffer, Gob, etc.
+    b, err := json.Marshal(ExamplePayload{UserID: 42})
+    if err != nil {
+        log.Fatal(err)
+    }
+
+    task := asynq.NewTask("example", b)
 
     // Enqueue the task to be processed immediately.
-    res, err := client.Enqueue(t)
+    res, err := client.Enqueue(task)
 
     // Schedule the task to be processed after one minute.
     res, err = client.Enqueue(t, asynq.ProcessIn(1*time.Minute))
@@ -52,10 +56,13 @@ Example of a type that implements the Handler interface.
 
     func (h *TaskHandler) ProcessTask(ctx context.Context, task *asynq.Task) error {
         switch task.Type {
-        case "send_email":
-            id, err := task.Payload.GetInt("user_id")
-            // send email
-        //...
+        case "example":
+            var data ExamplePayload
+            if err := json.Unmarshal(task.Payload(), &data); err != nil {
+                return err
+            }
+            // perform task with the data
+
         default:
             return fmt.Errorf("unexpected task type %q", task.Type)
         }
diff --git a/inspeq/inspector_test.go b/inspeq/inspector_test.go
index 6120ddf..0fedc9f 100644
--- a/inspeq/inspector_test.go
+++ b/inspeq/inspector_test.go
@@ -574,7 +574,7 @@ func TestInspectorListPendingTasks(t *testing.T) {
 				tc.desc, tc.qname, err)
 			continue
 		}
-		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Payload{})
+		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Task{})
 		if diff := cmp.Diff(tc.want, got, ignoreOpt); diff != "" {
 			t.Errorf("%s; ListPendingTasks(%q) = %v, want %v; (-want,+got)\n%s",
 				tc.desc, tc.qname, got, tc.want, diff)
@@ -632,7 +632,7 @@ func TestInspectorListActiveTasks(t *testing.T) {
 			t.Errorf("%s; ListActiveTasks(%q) returned error: %v", tc.qname, tc.desc, err)
 			continue
 		}
-		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Payload{})
+		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Task{})
 		if diff := cmp.Diff(tc.want, got, ignoreOpt); diff != "" {
 			t.Errorf("%s; ListActiveTask(%q) = %v, want %v; (-want,+got)\n%s",
 				tc.desc, tc.qname, got, tc.want, diff)
@@ -708,7 +708,7 @@ func TestInspectorListScheduledTasks(t *testing.T) {
 			t.Errorf("%s; ListScheduledTasks(%q) returned error: %v", tc.desc, tc.qname, err)
 			continue
 		}
-		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Payload{}, ScheduledTask{})
+		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Task{}, ScheduledTask{})
 		if diff := cmp.Diff(tc.want, got, ignoreOpt); diff != "" {
 			t.Errorf("%s; ListScheduledTask(%q) = %v, want %v; (-want,+got)\n%s",
 				tc.desc, tc.qname, got, tc.want, diff)
@@ -785,7 +785,7 @@ func TestInspectorListRetryTasks(t *testing.T) {
 			t.Errorf("%s; ListRetryTasks(%q) returned error: %v", tc.desc, tc.qname, err)
 			continue
 		}
-		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Payload{}, RetryTask{})
+		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Task{}, RetryTask{})
 		if diff := cmp.Diff(tc.want, got, ignoreOpt); diff != "" {
 			t.Errorf("%s; ListRetryTask(%q) = %v, want %v; (-want,+got)\n%s",
 				tc.desc, tc.qname, got, tc.want, diff)
@@ -861,7 +861,7 @@ func TestInspectorListArchivedTasks(t *testing.T) {
 			t.Errorf("%s; ListArchivedTasks(%q) returned error: %v", tc.desc, tc.qname, err)
 			continue
 		}
-		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Payload{}, ArchivedTask{})
+		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Task{}, ArchivedTask{})
 		if diff := cmp.Diff(tc.want, got, ignoreOpt); diff != "" {
 			t.Errorf("%s; ListArchivedTask(%q) = %v, want %v; (-want,+got)\n%s",
 				tc.desc, tc.qname, got, tc.want, diff)
@@ -922,7 +922,7 @@ func TestInspectorListPagination(t *testing.T) {
 			t.Errorf("ListPendingTask('default') returned error: %v", err)
 			continue
 		}
-		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Payload{})
+		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Task{})
 		if diff := cmp.Diff(tc.want, got, ignoreOpt); diff != "" {
 			t.Errorf("ListPendingTask('default') = %v, want %v; (-want,+got)\n%s",
 				got, tc.want, diff)
@@ -2598,7 +2598,7 @@ func TestInspectorSchedulerEntries(t *testing.T) {
 				{
 					Spec:    "@every 20m",
 					Type:    "bar",
-					Payload: map[string]interface{}{"fiz": "baz"},
+					Payload: h.JSON(map[string]interface{}{"fiz": "baz"}),
 					Opts:    []string{`Queue("bar")`, `MaxRetry(20)`},
 					Next:    now.Add(1 * time.Minute),
 					Prev:    now.Add(-19 * time.Minute),
@@ -2614,7 +2614,7 @@ func TestInspectorSchedulerEntries(t *testing.T) {
 				},
 				{
 					Spec: "@every 20m",
-					Task: asynq.NewTask("bar", map[string]interface{}{"fiz": "baz"}),
+					Task: asynq.NewTask("bar", h.JSON(map[string]interface{}{"fiz": "baz"})),
 					Opts: []asynq.Option{asynq.Queue("bar"), asynq.MaxRetry(20)},
 					Next: now.Add(1 * time.Minute),
 					Prev: now.Add(-19 * time.Minute),
@@ -2634,7 +2634,7 @@ func TestInspectorSchedulerEntries(t *testing.T) {
 			t.Errorf("SchedulerEntries() returned error: %v", err)
 			continue
 		}
-		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Payload{})
+		ignoreOpt := cmpopts.IgnoreUnexported(asynq.Task{})
 		if diff := cmp.Diff(tc.want, got, sortSchedulerEntry, ignoreOpt); diff != "" {
 			t.Errorf("SchedulerEntries() = %v, want %v; (-want,+got)\n%s",
 				got, tc.want, diff)
diff --git a/internal/asynqtest/asynqtest.go b/internal/asynqtest/asynqtest.go
index 7b1743d..66831ba 100644
--- a/internal/asynqtest/asynqtest.go
+++ b/internal/asynqtest/asynqtest.go
@@ -6,6 +6,7 @@
 package asynqtest
 
 import (
+	"encoding/json"
 	"math"
 	"sort"
 	"testing"
@@ -93,13 +94,13 @@ var SortStringSliceOpt = cmp.Transformer("SortStringSlice", func(in []string) []
 var IgnoreIDOpt = cmpopts.IgnoreFields(base.TaskMessage{}, "ID")
 
 // NewTaskMessage returns a new instance of TaskMessage given a task type and payload.
-func NewTaskMessage(taskType string, payload map[string]interface{}) *base.TaskMessage {
+func NewTaskMessage(taskType string, payload []byte) *base.TaskMessage {
 	return NewTaskMessageWithQueue(taskType, payload, base.DefaultQueueName)
 }
 
 // NewTaskMessageWithQueue returns a new instance of TaskMessage given a
 // task type, payload and queue name.
-func NewTaskMessageWithQueue(taskType string, payload map[string]interface{}, qname string) *base.TaskMessage {
+func NewTaskMessageWithQueue(taskType string, payload []byte, qname string) *base.TaskMessage {
 	return &base.TaskMessage{
 		ID:       uuid.New(),
 		Type:     taskType,
@@ -111,6 +112,15 @@ func NewTaskMessageWithQueue(taskType string, payload map[string]interface{}, qn
 	}
 }
 
+// JSON serializes the given key-value pairs into stream of bytes in JSON.
+func JSON(kv map[string]interface{}) []byte {
+	b, err := json.Marshal(kv)
+	if err != nil {
+		panic(err)
+	}
+	return b
+}
+
 // TaskMessageAfterRetry returns an updated copy of t after retry.
 // It increments retry count and sets the error message.
 func TaskMessageAfterRetry(t base.TaskMessage, errMsg string) *base.TaskMessage {
diff --git a/internal/base/base.go b/internal/base/base.go
index 6ac3f42..2b040af 100644
--- a/internal/base/base.go
+++ b/internal/base/base.go
@@ -6,12 +6,8 @@
 package base
 
 import (
-	"bytes"
 	"context"
-	"encoding/json"
 	"fmt"
-	"sort"
-	"strings"
 	"sync"
 	"time"
 
@@ -125,32 +121,8 @@ func SchedulerHistoryKey(entryID string) string {
 }
 
 // UniqueKey returns a redis key with the given type, payload, and queue name.
-func UniqueKey(qname, tasktype string, payload map[string]interface{}) string {
-	return fmt.Sprintf("asynq:{%s}:unique:%s:%s", qname, tasktype, serializePayload(payload))
-}
-
-func serializePayload(payload map[string]interface{}) string {
-	if payload == nil {
-		return "nil"
-	}
-	type entry struct {
-		k string
-		v interface{}
-	}
-	var es []entry
-	for k, v := range payload {
-		es = append(es, entry{k, v})
-	}
-	// sort entries by key
-	sort.Slice(es, func(i, j int) bool { return es[i].k < es[j].k })
-	var b strings.Builder
-	for _, e := range es {
-		if b.Len() > 0 {
-			b.WriteString(",")
-		}
-		b.WriteString(fmt.Sprintf("%s=%v", e.k, e.v))
-	}
-	return b.String()
+func UniqueKey(qname, tasktype string, payload []byte) string {
+	return fmt.Sprintf("asynq:{%s}:unique:%s:%s", qname, tasktype, string(payload))
 }
 
 // TaskMessage is the internal representation of a task with additional metadata fields.
@@ -160,7 +132,7 @@ type TaskMessage struct {
 	Type string
 
 	// Payload holds data needed to process the task.
-	Payload map[string]interface{}
+	Payload []byte
 
 	// ID is a unique identifier for each task.
 	ID uuid.UUID
@@ -203,13 +175,9 @@ func EncodeMessage(msg *TaskMessage) ([]byte, error) {
 	if msg == nil {
 		return nil, fmt.Errorf("cannot encode nil message")
 	}
-	payload, err := json.Marshal(msg.Payload)
-	if err != nil {
-		return nil, err
-	}
 	return proto.Marshal(&pb.TaskMessage{
 		Type:      msg.Type,
-		Payload:   payload,
+		Payload:   msg.Payload,
 		Id:        msg.ID.String(),
 		Queue:     msg.Queue,
 		Retry:     int32(msg.Retry),
@@ -227,13 +195,9 @@ func DecodeMessage(data []byte) (*TaskMessage, error) {
 	if err := proto.Unmarshal(data, &pbmsg); err != nil {
 		return nil, err
 	}
-	payload, err := decodePayload(pbmsg.GetPayload())
-	if err != nil {
-		return nil, err
-	}
 	return &TaskMessage{
 		Type:      pbmsg.GetType(),
-		Payload:   payload,
+		Payload:   pbmsg.GetPayload(),
 		ID:        uuid.MustParse(pbmsg.GetId()),
 		Queue:     pbmsg.GetQueue(),
 		Retry:     int(pbmsg.GetRetry()),
@@ -383,7 +347,7 @@ type WorkerInfo struct {
 	ServerID string
 	ID       string
 	Type     string
-	Payload  map[string]interface{}
+	Payload  []byte
 	Queue    string
 	Started  time.Time
 	Deadline time.Time
@@ -394,10 +358,6 @@ func EncodeWorkerInfo(info *WorkerInfo) ([]byte, error) {
 	if info == nil {
 		return nil, fmt.Errorf("cannot encode nil worker info")
 	}
-	payload, err := json.Marshal(info.Payload)
-	if err != nil {
-		return nil, err
-	}
 	startTime, err := ptypes.TimestampProto(info.Started)
 	if err != nil {
 		return nil, err
@@ -412,33 +372,19 @@ func EncodeWorkerInfo(info *WorkerInfo) ([]byte, error) {
 		ServerId:    info.ServerID,
 		TaskId:      info.ID,
 		TaskType:    info.Type,
-		TaskPayload: payload,
+		TaskPayload: info.Payload,
 		Queue:       info.Queue,
 		StartTime:   startTime,
 		Deadline:    deadline,
 	})
 }
 
-func decodePayload(b []byte) (map[string]interface{}, error) {
-	d := json.NewDecoder(bytes.NewReader(b))
-	d.UseNumber()
-	payload := make(map[string]interface{})
-	if err := d.Decode(&payload); err != nil {
-		return nil, err
-	}
-	return payload, nil
-}
-
 // DecodeWorkerInfo decodes the given bytes into WorkerInfo.
 func DecodeWorkerInfo(b []byte) (*WorkerInfo, error) {
 	var pbmsg pb.WorkerInfo
 	if err := proto.Unmarshal(b, &pbmsg); err != nil {
 		return nil, err
 	}
-	payload, err := decodePayload(pbmsg.GetTaskPayload())
-	if err != nil {
-		return nil, err
-	}
 	startTime, err := ptypes.Timestamp(pbmsg.GetStartTime())
 	if err != nil {
 		return nil, err
@@ -453,7 +399,7 @@ func DecodeWorkerInfo(b []byte) (*WorkerInfo, error) {
 		ServerID: pbmsg.GetServerId(),
 		ID:       pbmsg.GetTaskId(),
 		Type:     pbmsg.GetTaskType(),
-		Payload:  payload,
+		Payload:  pbmsg.GetTaskPayload(),
 		Queue:    pbmsg.GetQueue(),
 		Started:  startTime,
 		Deadline: deadline,
@@ -472,7 +418,7 @@ type SchedulerEntry struct {
 	Type string
 
 	// Payload is the payload of the periodic task.
-	Payload map[string]interface{}
+	Payload []byte
 
 	// Opts is the options for the periodic task.
 	Opts []string
@@ -490,10 +436,6 @@ func EncodeSchedulerEntry(entry *SchedulerEntry) ([]byte, error) {
 	if entry == nil {
 		return nil, fmt.Errorf("cannot encode nil scheduler entry")
 	}
-	payload, err := json.Marshal(entry.Payload)
-	if err != nil {
-		return nil, err
-	}
 	next, err := ptypes.TimestampProto(entry.Next)
 	if err != nil {
 		return nil, err
@@ -506,7 +448,7 @@ func EncodeSchedulerEntry(entry *SchedulerEntry) ([]byte, error) {
 		Id:              entry.ID,
 		Spec:            entry.Spec,
 		TaskType:        entry.Type,
-		TaskPayload:     payload,
+		TaskPayload:     entry.Payload,
 		EnqueueOptions:  entry.Opts,
 		NextEnqueueTime: next,
 		PrevEnqueueTime: prev,
@@ -519,10 +461,6 @@ func DecodeSchedulerEntry(b []byte) (*SchedulerEntry, error) {
 	if err := proto.Unmarshal(b, &pbmsg); err != nil {
 		return nil, err
 	}
-	payload, err := decodePayload(pbmsg.GetTaskPayload())
-	if err != nil {
-		return nil, err
-	}
 	next, err := ptypes.Timestamp(pbmsg.GetNextEnqueueTime())
 	if err != nil {
 		return nil, err
@@ -535,7 +473,7 @@ func DecodeSchedulerEntry(b []byte) (*SchedulerEntry, error) {
 		ID:      pbmsg.GetId(),
 		Spec:    pbmsg.GetSpec(),
 		Type:    pbmsg.GetTaskType(),
-		Payload: payload,
+		Payload: pbmsg.GetTaskPayload(),
 		Opts:    pbmsg.GetEnqueueOptions(),
 		Next:    next,
 		Prev:    prev,
diff --git a/internal/base/base_test.go b/internal/base/base_test.go
index bfebef5..cd8baea 100644
--- a/internal/base/base_test.go
+++ b/internal/base/base_test.go
@@ -267,52 +267,68 @@ func TestSchedulerHistoryKey(t *testing.T) {
 	}
 }
 
+func toBytes(m map[string]interface{}) []byte {
+	b, err := json.Marshal(m)
+	if err != nil {
+		panic(err)
+	}
+	return b
+}
+
 func TestUniqueKey(t *testing.T) {
 	tests := []struct {
 		desc     string
 		qname    string
 		tasktype string
-		payload  map[string]interface{}
+		payload  []byte
 		want     string
 	}{
 		{
 			"with primitive types",
 			"default",
 			"email:send",
-			map[string]interface{}{"a": 123, "b": "hello", "c": true},
-			"asynq:{default}:unique:email:send:a=123,b=hello,c=true",
+			toBytes(map[string]interface{}{"a": 123, "b": "hello", "c": true}),
+			fmt.Sprintf("asynq:{default}:unique:email:send:%s",
+				string(toBytes(map[string]interface{}{"a": 123, "b": "hello", "c": true}))),
 		},
 		{
 			"with unsorted keys",
 			"default",
 			"email:send",
-			map[string]interface{}{"b": "hello", "c": true, "a": 123},
-			"asynq:{default}:unique:email:send:a=123,b=hello,c=true",
+			toBytes(map[string]interface{}{"b": "hello", "c": true, "a": 123}),
+			fmt.Sprintf("asynq:{default}:unique:email:send:%s",
+				string(toBytes(map[string]interface{}{"b": "hello", "c": true, "a": 123}))),
 		},
 		{
 			"with composite types",
 			"default",
 			"email:send",
-			map[string]interface{}{
+			toBytes(map[string]interface{}{
 				"address": map[string]string{"line": "123 Main St", "city": "Boston", "state": "MA"},
-				"names":   []string{"bob", "mike", "rob"}},
-			"asynq:{default}:unique:email:send:address=map[city:Boston line:123 Main St state:MA],names=[bob mike rob]",
+				"names":   []string{"bob", "mike", "rob"}}),
+			fmt.Sprintf("asynq:{default}:unique:email:send:%s",
+				string(toBytes(map[string]interface{}{
+					"address": map[string]string{"line": "123 Main St", "city": "Boston", "state": "MA"},
+					"names":   []string{"bob", "mike", "rob"}}))),
 		},
 		{
 			"with complex types",
 			"default",
 			"email:send",
-			map[string]interface{}{
+			toBytes(map[string]interface{}{
 				"time":     time.Date(2020, time.July, 28, 0, 0, 0, 0, time.UTC),
-				"duration": time.Hour},
-			"asynq:{default}:unique:email:send:duration=1h0m0s,time=2020-07-28 00:00:00 +0000 UTC",
+				"duration": time.Hour}),
+			fmt.Sprintf("asynq:{default}:unique:email:send:%s",
+				string(toBytes(map[string]interface{}{
+					"time":     time.Date(2020, time.July, 28, 0, 0, 0, 0, time.UTC),
+					"duration": time.Hour}))),
 		},
 		{
 			"with nil payload",
 			"default",
 			"reindex",
 			nil,
-			"asynq:{default}:unique:reindex:nil",
+			"asynq:{default}:unique:reindex:",
 		},
 	}
 
@@ -333,7 +349,7 @@ func TestMessageEncoding(t *testing.T) {
 		{
 			in: &TaskMessage{
 				Type:     "task1",
-				Payload:  map[string]interface{}{"a": 1, "b": "hello!", "c": true},
+				Payload:  toBytes(map[string]interface{}{"a": 1, "b": "hello!", "c": true}),
 				ID:       id,
 				Queue:    "default",
 				Retry:    10,
@@ -343,7 +359,7 @@ func TestMessageEncoding(t *testing.T) {
 			},
 			out: &TaskMessage{
 				Type:     "task1",
-				Payload:  map[string]interface{}{"a": json.Number("1"), "b": "hello!", "c": true},
+				Payload:  toBytes(map[string]interface{}{"a": json.Number("1"), "b": "hello!", "c": true}),
 				ID:       id,
 				Queue:    "default",
 				Retry:    10,
@@ -420,7 +436,7 @@ func TestWorkerInfoEncoding(t *testing.T) {
 				ServerID: "abc123",
 				ID:       uuid.NewString(),
 				Type:     "taskA",
-				Payload:  map[string]interface{}{"foo": "bar"},
+				Payload:  toBytes(map[string]interface{}{"foo": "bar"}),
 				Queue:    "default",
 				Started:  time.Now().Add(-3 * time.Hour),
 				Deadline: time.Now().Add(30 * time.Second),
@@ -455,7 +471,7 @@ func TestSchedulerEntryEncoding(t *testing.T) {
 				ID:      uuid.NewString(),
 				Spec:    "* * * * *",
 				Type:    "task_A",
-				Payload: map[string]interface{}{"foo": "bar"},
+				Payload: toBytes(map[string]interface{}{"foo": "bar"}),
 				Opts:    []string{"Queue('email')"},
 				Next:    time.Now().Add(30 * time.Second).UTC(),
 				Prev:    time.Now().Add(-2 * time.Minute).UTC(),
diff --git a/internal/rdb/inspect_test.go b/internal/rdb/inspect_test.go
index 0999af2..1b50df1 100644
--- a/internal/rdb/inspect_test.go
+++ b/internal/rdb/inspect_test.go
@@ -50,9 +50,9 @@ func TestAllQueues(t *testing.T) {
 func TestCurrentStats(t *testing.T) {
 	r := setup(t)
 	defer r.Close()
-	m1 := h.NewTaskMessage("send_email", map[string]interface{}{"subject": "hello"})
+	m1 := h.NewTaskMessage("send_email", h.JSON(map[string]interface{}{"subject": "hello"}))
 	m2 := h.NewTaskMessage("reindex", nil)
-	m3 := h.NewTaskMessage("gen_thumbnail", map[string]interface{}{"src": "some/path/to/img"})
+	m3 := h.NewTaskMessage("gen_thumbnail", h.JSON(map[string]interface{}{"src": "some/path/to/img"}))
 	m4 := h.NewTaskMessage("sync", nil)
 	m5 := h.NewTaskMessageWithQueue("important_notification", nil, "critical")
 	m6 := h.NewTaskMessageWithQueue("minor_notification", nil, "low")
@@ -312,7 +312,7 @@ func TestListPending(t *testing.T) {
 	r := setup(t)
 	defer r.Close()
 
-	m1 := h.NewTaskMessage("send_email", map[string]interface{}{"subject": "hello"})
+	m1 := h.NewTaskMessage("send_email", h.JSON(map[string]interface{}{"subject": "hello"}))
 	m2 := h.NewTaskMessage("reindex", nil)
 	m3 := h.NewTaskMessageWithQueue("important_notification", nil, "critical")
 	m4 := h.NewTaskMessageWithQueue("minor_notification", nil, "low")
@@ -3365,9 +3365,9 @@ func TestListWorkers(t *testing.T) {
 		pid      = 4567
 		serverID = "server123"
 
-		m1 = h.NewTaskMessage("send_email", map[string]interface{}{"user_id": "abc123"})
-		m2 = h.NewTaskMessage("gen_thumbnail", map[string]interface{}{"path": "some/path/to/image/file"})
-		m3 = h.NewTaskMessage("reindex", map[string]interface{}{})
+		m1 = h.NewTaskMessage("send_email", h.JSON(map[string]interface{}{"user_id": "abc123"}))
+		m2 = h.NewTaskMessage("gen_thumbnail", h.JSON(map[string]interface{}{"path": "some/path/to/image/file"}))
+		m3 = h.NewTaskMessage("reindex", h.JSON(map[string]interface{}{}))
 	)
 
 	tests := []struct {
@@ -3450,7 +3450,7 @@ func TestWriteListClearSchedulerEntries(t *testing.T) {
 		{
 			Spec:    "@every 20m",
 			Type:    "bar",
-			Payload: map[string]interface{}{"fiz": "baz"},
+			Payload: h.JSON(map[string]interface{}{"fiz": "baz"}),
 			Opts:    nil,
 			Next:    now.Add(1 * time.Minute),
 			Prev:    now.Add(-19 * time.Minute),
diff --git a/internal/rdb/rdb_test.go b/internal/rdb/rdb_test.go
index 23c32ea..b936360 100644
--- a/internal/rdb/rdb_test.go
+++ b/internal/rdb/rdb_test.go
@@ -61,8 +61,8 @@ func setup(tb testing.TB) (r *RDB) {
 func TestEnqueue(t *testing.T) {
 	r := setup(t)
 	defer r.Close()
-	t1 := h.NewTaskMessage("send_email", map[string]interface{}{"to": "exampleuser@gmail.com", "from": "noreply@example.com"})
-	t2 := h.NewTaskMessageWithQueue("generate_csv", map[string]interface{}{}, "csv")
+	t1 := h.NewTaskMessage("send_email", h.JSON(map[string]interface{}{"to": "exampleuser@gmail.com", "from": "noreply@example.com"}))
+	t2 := h.NewTaskMessageWithQueue("generate_csv", h.JSON(map[string]interface{}{}), "csv")
 	t3 := h.NewTaskMessageWithQueue("sync", nil, "low")
 
 	tests := []struct {
@@ -101,9 +101,9 @@ func TestEnqueueUnique(t *testing.T) {
 	m1 := base.TaskMessage{
 		ID:        uuid.New(),
 		Type:      "email",
-		Payload:   map[string]interface{}{"user_id": json.Number("123")},
+		Payload:   h.JSON(map[string]interface{}{"user_id": json.Number("123")}),
 		Queue:     base.DefaultQueueName,
-		UniqueKey: base.UniqueKey(base.DefaultQueueName, "email", map[string]interface{}{"user_id": 123}),
+		UniqueKey: base.UniqueKey(base.DefaultQueueName, "email", h.JSON(map[string]interface{}{"user_id": 123})),
 	}
 
 	tests := []struct {
@@ -157,7 +157,7 @@ func TestDequeue(t *testing.T) {
 	t1 := &base.TaskMessage{
 		ID:       uuid.New(),
 		Type:     "send_email",
-		Payload:  map[string]interface{}{"subject": "hello!"},
+		Payload:  h.JSON(map[string]interface{}{"subject": "hello!"}),
 		Queue:    "default",
 		Timeout:  1800,
 		Deadline: 0,
@@ -355,7 +355,7 @@ func TestDequeueIgnoresPausedQueues(t *testing.T) {
 	t1 := &base.TaskMessage{
 		ID:       uuid.New(),
 		Type:     "send_email",
-		Payload:  map[string]interface{}{"subject": "hello!"},
+		Payload:  h.JSON(map[string]interface{}{"subject": "hello!"}),
 		Queue:    "default",
 		Timeout:  1800,
 		Deadline: 0,
@@ -767,7 +767,7 @@ func TestRequeue(t *testing.T) {
 func TestSchedule(t *testing.T) {
 	r := setup(t)
 	defer r.Close()
-	msg := h.NewTaskMessage("send_email", map[string]interface{}{"subject": "hello"})
+	msg := h.NewTaskMessage("send_email", h.JSON(map[string]interface{}{"subject": "hello"}))
 	tests := []struct {
 		msg       *base.TaskMessage
 		processAt time.Time
@@ -808,9 +808,9 @@ func TestScheduleUnique(t *testing.T) {
 	m1 := base.TaskMessage{
 		ID:        uuid.New(),
 		Type:      "email",
-		Payload:   map[string]interface{}{"user_id": 123},
+		Payload:   h.JSON(map[string]interface{}{"user_id": 123}),
 		Queue:     base.DefaultQueueName,
-		UniqueKey: base.UniqueKey(base.DefaultQueueName, "email", map[string]interface{}{"user_id": 123}),
+		UniqueKey: base.UniqueKey(base.DefaultQueueName, "email", h.JSON(map[string]interface{}{"user_id": 123})),
 	}
 
 	tests := []struct {
@@ -866,7 +866,7 @@ func TestRetry(t *testing.T) {
 	t1 := &base.TaskMessage{
 		ID:      uuid.New(),
 		Type:    "send_email",
-		Payload: map[string]interface{}{"subject": "Hola!"},
+		Payload: h.JSON(map[string]interface{}{"subject": "Hola!"}),
 		Retried: 10,
 		Timeout: 1800,
 		Queue:   "default",
@@ -874,7 +874,7 @@ func TestRetry(t *testing.T) {
 	t2 := &base.TaskMessage{
 		ID:      uuid.New(),
 		Type:    "gen_thumbnail",
-		Payload: map[string]interface{}{"path": "some/path/to/image.jpg"},
+		Payload: h.JSON(map[string]interface{}{"path": "some/path/to/image.jpg"}),
 		Timeout: 3000,
 		Queue:   "default",
 	}
@@ -1530,8 +1530,8 @@ func TestWriteServerStateWithWorkers(t *testing.T) {
 		pid      = 4242
 		serverID = "server123"
 
-		msg1 = h.NewTaskMessage("send_email", map[string]interface{}{"user_id": "123"})
-		msg2 = h.NewTaskMessage("gen_thumbnail", map[string]interface{}{"path": "some/path/to/imgfile"})
+		msg1 = h.NewTaskMessage("send_email", h.JSON(map[string]interface{}{"user_id": "123"}))
+		msg2 = h.NewTaskMessage("gen_thumbnail", h.JSON(map[string]interface{}{"path": "some/path/to/imgfile"}))
 
 		ttl = 5 * time.Second
 	)
@@ -1642,8 +1642,8 @@ func TestClearServerState(t *testing.T) {
 		otherPID      = 9876
 		otherServerID = "server987"
 
-		msg1 = h.NewTaskMessage("send_email", map[string]interface{}{"user_id": "123"})
-		msg2 = h.NewTaskMessage("gen_thumbnail", map[string]interface{}{"path": "some/path/to/imgfile"})
+		msg1 = h.NewTaskMessage("send_email", h.JSON(map[string]interface{}{"user_id": "123"}))
+		msg2 = h.NewTaskMessage("gen_thumbnail", h.JSON(map[string]interface{}{"path": "some/path/to/imgfile"}))
 
 		ttl = 5 * time.Second
 	)
diff --git a/payload.go b/payload.go
deleted file mode 100644
index b447ef9..0000000
--- a/payload.go
+++ /dev/null
@@ -1,230 +0,0 @@
-// Copyright 2020 Kentaro Hibino. All rights reserved.
-// Use of this source code is governed by a MIT license
-// that can be found in the LICENSE file.
-
-package asynq
-
-import (
-	"encoding/json"
-	"fmt"
-	"time"
-
-	"github.com/spf13/cast"
-)
-
-// Payload holds arbitrary data needed for task execution.
-type Payload struct {
-	data map[string]interface{}
-}
-
-type errKeyNotFound struct {
-	key string
-}
-
-func (e *errKeyNotFound) Error() string {
-	return fmt.Sprintf("key %q does not exist", e.key)
-}
-
-// Has reports whether key exists.
-func (p Payload) Has(key string) bool {
-	_, ok := p.data[key]
-	return ok
-}
-
-func toInt(v interface{}) (int, error) {
-	switch v := v.(type) {
-	case json.Number:
-		val, err := v.Int64()
-		if err != nil {
-			return 0, err
-		}
-		return int(val), nil
-	default:
-		return cast.ToIntE(v)
-	}
-}
-
-// String returns a string representation of payload data.
-func (p Payload) String() string {
-	return fmt.Sprint(p.data)
-}
-
-// MarshalJSON returns the JSON encoding of payload data.
-func (p Payload) MarshalJSON() ([]byte, error) {
-	return json.Marshal(p.data)
-}
-
-// GetString returns a string value if a string type is associated with
-// the key, otherwise reports an error.
-func (p Payload) GetString(key string) (string, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return "", &errKeyNotFound{key}
-	}
-	return cast.ToStringE(v)
-}
-
-// GetInt returns an int value if a numeric type is associated with
-// the key, otherwise reports an error.
-func (p Payload) GetInt(key string) (int, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return 0, &errKeyNotFound{key}
-	}
-	return toInt(v)
-}
-
-// GetFloat64 returns a float64 value if a numeric type is associated with
-// the key, otherwise reports an error.
-func (p Payload) GetFloat64(key string) (float64, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return 0, &errKeyNotFound{key}
-	}
-	switch v := v.(type) {
-	case json.Number:
-		return v.Float64()
-	default:
-		return cast.ToFloat64E(v)
-	}
-}
-
-// GetBool returns a boolean value if a boolean type is associated with
-// the key, otherwise reports an error.
-func (p Payload) GetBool(key string) (bool, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return false, &errKeyNotFound{key}
-	}
-	return cast.ToBoolE(v)
-}
-
-// GetStringSlice returns a slice of strings if a string slice type is associated with
-// the key, otherwise reports an error.
-func (p Payload) GetStringSlice(key string) ([]string, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return nil, &errKeyNotFound{key}
-	}
-	return cast.ToStringSliceE(v)
-}
-
-// GetIntSlice returns a slice of ints if a int slice type is associated with
-// the key, otherwise reports an error.
-func (p Payload) GetIntSlice(key string) ([]int, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return nil, &errKeyNotFound{key}
-	}
-	switch v := v.(type) {
-	case []interface{}:
-		var res []int
-		for _, elem := range v {
-			val, err := toInt(elem)
-			if err != nil {
-				return nil, err
-			}
-			res = append(res, int(val))
-		}
-		return res, nil
-	default:
-		return cast.ToIntSliceE(v)
-	}
-}
-
-// GetStringMap returns a map of string to empty interface
-// if a correct map type is associated with the key,
-// otherwise reports an error.
-func (p Payload) GetStringMap(key string) (map[string]interface{}, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return nil, &errKeyNotFound{key}
-	}
-	return cast.ToStringMapE(v)
-}
-
-// GetStringMapString returns a map of string to string
-// if a correct map type is associated with the key,
-// otherwise reports an error.
-func (p Payload) GetStringMapString(key string) (map[string]string, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return nil, &errKeyNotFound{key}
-	}
-	return cast.ToStringMapStringE(v)
-}
-
-// GetStringMapStringSlice returns a map of string to string slice
-// if a correct map type is associated with the key,
-// otherwise reports an error.
-func (p Payload) GetStringMapStringSlice(key string) (map[string][]string, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return nil, &errKeyNotFound{key}
-	}
-	return cast.ToStringMapStringSliceE(v)
-}
-
-// GetStringMapInt returns a map of string to int
-// if a correct map type is associated with the key,
-// otherwise reports an error.
-func (p Payload) GetStringMapInt(key string) (map[string]int, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return nil, &errKeyNotFound{key}
-	}
-	switch v := v.(type) {
-	case map[string]interface{}:
-		res := make(map[string]int)
-		for key, val := range v {
-			ival, err := toInt(val)
-			if err != nil {
-				return nil, err
-			}
-			res[key] = ival
-		}
-		return res, nil
-	default:
-		return cast.ToStringMapIntE(v)
-	}
-}
-
-// GetStringMapBool returns a map of string to boolean
-// if a correct map type is associated with the key,
-// otherwise reports an error.
-func (p Payload) GetStringMapBool(key string) (map[string]bool, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return nil, &errKeyNotFound{key}
-	}
-	return cast.ToStringMapBoolE(v)
-}
-
-// GetTime returns a time value if a correct map type is associated with the key,
-// otherwise reports an error.
-func (p Payload) GetTime(key string) (time.Time, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return time.Time{}, &errKeyNotFound{key}
-	}
-	return cast.ToTimeE(v)
-}
-
-// GetDuration returns a duration value if a correct map type is associated with the key,
-// otherwise reports an error.
-func (p Payload) GetDuration(key string) (time.Duration, error) {
-	v, ok := p.data[key]
-	if !ok {
-		return 0, &errKeyNotFound{key}
-	}
-	switch v := v.(type) {
-	case json.Number:
-		val, err := v.Int64()
-		if err != nil {
-			return 0, err
-		}
-		return time.Duration(val), nil
-	default:
-		return cast.ToDurationE(v)
-	}
-}
diff --git a/payload_test.go b/payload_test.go
deleted file mode 100644
index 379a4ac..0000000
--- a/payload_test.go
+++ /dev/null
@@ -1,675 +0,0 @@
-// Copyright 2020 Kentaro Hibino. All rights reserved.
-// Use of this source code is governed by a MIT license
-// that can be found in the LICENSE file.
-
-package asynq
-
-import (
-	"encoding/json"
-	"fmt"
-	"testing"
-	"time"
-
-	"github.com/google/go-cmp/cmp"
-	"github.com/google/go-cmp/cmp/cmpopts"
-	h "github.com/hibiken/asynq/internal/asynqtest"
-	"github.com/hibiken/asynq/internal/base"
-)
-
-type payloadTest struct {
-	data   map[string]interface{}
-	key    string
-	nonkey string
-}
-
-func TestPayloadString(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"name": "gopher"},
-			key:    "name",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetString(tc.key)
-		if err != nil || got != tc.data[tc.key] {
-			t.Errorf("Payload.GetString(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetString(tc.key)
-		if err != nil || got != tc.data[tc.key] {
-			t.Errorf("With Marshaling: Payload.GetString(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetString(tc.nonkey)
-		if err == nil || got != "" {
-			t.Errorf("Payload.GetString(%q) = %v, %v; want '', error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadInt(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"user_id": 42},
-			key:    "user_id",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetInt(tc.key)
-		if err != nil || got != tc.data[tc.key] {
-			t.Errorf("Payload.GetInt(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetInt(tc.key)
-		if err != nil || got != tc.data[tc.key] {
-			t.Errorf("With Marshaling: Payload.GetInt(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetInt(tc.nonkey)
-		if err == nil || got != 0 {
-			t.Errorf("Payload.GetInt(%q) = %v, %v; want 0, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadFloat64(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"pi": 3.14},
-			key:    "pi",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetFloat64(tc.key)
-		if err != nil || got != tc.data[tc.key] {
-			t.Errorf("Payload.GetFloat64(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetFloat64(tc.key)
-		if err != nil || got != tc.data[tc.key] {
-			t.Errorf("With Marshaling: Payload.GetFloat64(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetFloat64(tc.nonkey)
-		if err == nil || got != 0 {
-			t.Errorf("Payload.GetFloat64(%q) = %v, %v; want 0, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadBool(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"enabled": true},
-			key:    "enabled",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetBool(tc.key)
-		if err != nil || got != tc.data[tc.key] {
-			t.Errorf("Payload.GetBool(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetBool(tc.key)
-		if err != nil || got != tc.data[tc.key] {
-			t.Errorf("With Marshaling: Payload.GetBool(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetBool(tc.nonkey)
-		if err == nil || got != false {
-			t.Errorf("Payload.GetBool(%q) = %v, %v; want false, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadStringSlice(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"names": []string{"luke", "rey", "anakin"}},
-			key:    "names",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetStringSlice(tc.key)
-		diff := cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("Payload.GetStringSlice(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetStringSlice(tc.key)
-		diff = cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("With Marshaling: Payload.GetStringSlice(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetStringSlice(tc.nonkey)
-		if err == nil || got != nil {
-			t.Errorf("Payload.GetStringSlice(%q) = %v, %v; want nil, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadIntSlice(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"nums": []int{9, 8, 7}},
-			key:    "nums",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetIntSlice(tc.key)
-		diff := cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("Payload.GetIntSlice(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetIntSlice(tc.key)
-		diff = cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("With Marshaling: Payload.GetIntSlice(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetIntSlice(tc.nonkey)
-		if err == nil || got != nil {
-			t.Errorf("Payload.GetIntSlice(%q) = %v, %v; want nil, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadStringMap(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"user": map[string]interface{}{"name": "Jon Doe", "score": 2.2}},
-			key:    "user",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetStringMap(tc.key)
-		diff := cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("Payload.GetStringMap(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetStringMap(tc.key)
-		ignoreOpt := cmpopts.IgnoreMapEntries(func(key string, val interface{}) bool {
-			switch val.(type) {
-			case json.Number:
-				return true
-			default:
-				return false
-			}
-		})
-		diff = cmp.Diff(got, tc.data[tc.key], ignoreOpt)
-		if err != nil || diff != "" {
-			t.Errorf("With Marshaling: Payload.GetStringMap(%q) = %v, %v, want %v, nil;(-want,+got)\n%s",
-				tc.key, got, err, tc.data[tc.key], diff)
-		}
-
-		// access non-existent key.
-		got, err = payload.GetStringMap(tc.nonkey)
-		if err == nil || got != nil {
-			t.Errorf("Payload.GetStringMap(%q) = %v, %v; want nil, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadStringMapString(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"address": map[string]string{"line": "123 Main St", "city": "San Francisco", "state": "CA"}},
-			key:    "address",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetStringMapString(tc.key)
-		diff := cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("Payload.GetStringMapString(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetStringMapString(tc.key)
-		diff = cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("With Marshaling: Payload.GetStringMapString(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetStringMapString(tc.nonkey)
-		if err == nil || got != nil {
-			t.Errorf("Payload.GetStringMapString(%q) = %v, %v; want nil, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadStringMapStringSlice(t *testing.T) {
-	favs := map[string][]string{
-		"movies":   {"forrest gump", "star wars"},
-		"tv_shows": {"game of thrones", "HIMYM", "breaking bad"},
-	}
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"favorites": favs},
-			key:    "favorites",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetStringMapStringSlice(tc.key)
-		diff := cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("Payload.GetStringMapStringSlice(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetStringMapStringSlice(tc.key)
-		diff = cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("With Marshaling: Payload.GetStringMapStringSlice(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetStringMapStringSlice(tc.nonkey)
-		if err == nil || got != nil {
-			t.Errorf("Payload.GetStringMapStringSlice(%q) = %v, %v; want nil, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadStringMapInt(t *testing.T) {
-	counter := map[string]int{
-		"a": 1,
-		"b": 101,
-		"c": 42,
-	}
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"counts": counter},
-			key:    "counts",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetStringMapInt(tc.key)
-		diff := cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("Payload.GetStringMapInt(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetStringMapInt(tc.key)
-		diff = cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("With Marshaling: Payload.GetStringMapInt(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetStringMapInt(tc.nonkey)
-		if err == nil || got != nil {
-			t.Errorf("Payload.GetStringMapInt(%q) = %v, %v; want nil, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadStringMapBool(t *testing.T) {
-	features := map[string]bool{
-		"A": false,
-		"B": true,
-		"C": true,
-	}
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"features": features},
-			key:    "features",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetStringMapBool(tc.key)
-		diff := cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("Payload.GetStringMapBool(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetStringMapBool(tc.key)
-		diff = cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("With Marshaling: Payload.GetStringMapBool(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetStringMapBool(tc.nonkey)
-		if err == nil || got != nil {
-			t.Errorf("Payload.GetStringMapBool(%q) = %v, %v; want nil, error",
-				tc.key, got, err)
-		}
-	}
-}
-
-func TestPayloadTime(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"current": time.Now()},
-			key:    "current",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetTime(tc.key)
-		diff := cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("Payload.GetTime(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetTime(tc.key)
-		diff = cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("With Marshaling: Payload.GetTime(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetTime(tc.nonkey)
-		if err == nil || !got.IsZero() {
-			t.Errorf("Payload.GetTime(%q) = %v, %v; want %v, error",
-				tc.key, got, err, time.Time{})
-		}
-	}
-}
-
-func TestPayloadDuration(t *testing.T) {
-	tests := []payloadTest{
-		{
-			data:   map[string]interface{}{"duration": 15 * time.Minute},
-			key:    "duration",
-			nonkey: "unknown",
-		},
-	}
-
-	for _, tc := range tests {
-		payload := Payload{tc.data}
-
-		got, err := payload.GetDuration(tc.key)
-		diff := cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("Payload.GetDuration(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// encode and then decode task messsage.
-		in := h.NewTaskMessage("testing", tc.data)
-		encoded, err := base.EncodeMessage(in)
-		if err != nil {
-			t.Fatal(err)
-		}
-		out, err := base.DecodeMessage(encoded)
-		if err != nil {
-			t.Fatal(err)
-		}
-		payload = Payload{out.Payload}
-		got, err = payload.GetDuration(tc.key)
-		diff = cmp.Diff(got, tc.data[tc.key])
-		if err != nil || diff != "" {
-			t.Errorf("With Marshaling: Payload.GetDuration(%q) = %v, %v, want %v, nil",
-				tc.key, got, err, tc.data[tc.key])
-		}
-
-		// access non-existent key.
-		got, err = payload.GetDuration(tc.nonkey)
-		if err == nil || got != 0 {
-			t.Errorf("Payload.GetDuration(%q) = %v, %v; want %v, error",
-				tc.key, got, err, time.Duration(0))
-		}
-	}
-}
-
-func TestPayloadHas(t *testing.T) {
-	payload := Payload{map[string]interface{}{
-		"user_id": 123,
-	}}
-
-	if !payload.Has("user_id") {
-		t.Errorf("Payload.Has(%q) = false, want true", "user_id")
-	}
-	if payload.Has("name") {
-		t.Errorf("Payload.Has(%q) = true, want false", "name")
-	}
-}
-
-func TestPayloadDebuggingStrings(t *testing.T) {
-	data := map[string]interface{}{
-		"foo": 123,
-		"bar": "hello",
-		"baz": false,
-	}
-	payload := Payload{data: data}
-
-	if payload.String() != fmt.Sprint(data) {
-		t.Errorf("Payload.String() = %q, want %q",
-			payload.String(), fmt.Sprint(data))
-	}
-
-	got, err := payload.MarshalJSON()
-	if err != nil {
-		t.Fatal(err)
-	}
-	want, err := json.Marshal(data)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if diff := cmp.Diff(got, want); diff != "" {
-		t.Errorf("Payload.MarhsalJSON() = %s, want %s; (-want,+got)\n%s",
-			got, want, diff)
-	}
-}
diff --git a/processor_test.go b/processor_test.go
index 7475889..6fd3f25 100644
--- a/processor_test.go
+++ b/processor_test.go
@@ -6,6 +6,7 @@ package asynq
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"sort"
 	"sync"
@@ -13,7 +14,6 @@ import (
 	"time"
 
 	"github.com/google/go-cmp/cmp"
-	"github.com/google/go-cmp/cmp/cmpopts"
 	h "github.com/hibiken/asynq/internal/asynqtest"
 	"github.com/hibiken/asynq/internal/base"
 	"github.com/hibiken/asynq/internal/rdb"
@@ -124,7 +124,7 @@ func TestProcessorSuccessWithSingleQueue(t *testing.T) {
 		p.terminate()
 
 		mu.Lock()
-		if diff := cmp.Diff(tc.wantProcessed, processed, sortTaskOpt, cmp.AllowUnexported(Payload{})); diff != "" {
+		if diff := cmp.Diff(tc.wantProcessed, processed, sortTaskOpt, cmp.AllowUnexported(Task{})); diff != "" {
 			t.Errorf("mismatch found in processed tasks; (-want, +got)\n%s", diff)
 		}
 		mu.Unlock()
@@ -216,7 +216,7 @@ func TestProcessorSuccessWithMultipleQueues(t *testing.T) {
 		p.terminate()
 
 		mu.Lock()
-		if diff := cmp.Diff(tc.wantProcessed, processed, sortTaskOpt, cmp.AllowUnexported(Payload{})); diff != "" {
+		if diff := cmp.Diff(tc.wantProcessed, processed, sortTaskOpt, cmp.AllowUnexported(Task{})); diff != "" {
 			t.Errorf("mismatch found in processed tasks; (-want, +got)\n%s", diff)
 		}
 		mu.Unlock()
@@ -228,7 +228,7 @@ func TestProcessTasksWithLargeNumberInPayload(t *testing.T) {
 	r := setup(t)
 	rdbClient := rdb.NewRDB(r)
 
-	m1 := h.NewTaskMessage("large_number", map[string]interface{}{"data": 111111111111111111})
+	m1 := h.NewTaskMessage("large_number", h.JSON(map[string]interface{}{"data": 111111111111111111}))
 	t1 := NewTask(m1.Type, m1.Payload)
 
 	tests := []struct {
@@ -250,10 +250,14 @@ func TestProcessTasksWithLargeNumberInPayload(t *testing.T) {
 		handler := func(ctx context.Context, task *Task) error {
 			mu.Lock()
 			defer mu.Unlock()
-			if data, err := task.Payload.GetInt("data"); err != nil {
-				t.Errorf("coult not get data from payload: %v", err)
-			} else {
+			var payload map[string]int
+			if err := json.Unmarshal(task.Payload(), &payload); err != nil {
+				t.Errorf("coult not decode payload: %v", err)
+			}
+			if data, ok := payload["data"]; ok {
 				t.Logf("data == %d", data)
+			} else {
+				t.Errorf("could not get data from payload")
 			}
 			processed = append(processed, task)
 			return nil
@@ -289,7 +293,7 @@ func TestProcessTasksWithLargeNumberInPayload(t *testing.T) {
 		p.terminate()
 
 		mu.Lock()
-		if diff := cmp.Diff(tc.wantProcessed, processed, sortTaskOpt, cmpopts.IgnoreUnexported(Payload{})); diff != "" {
+		if diff := cmp.Diff(tc.wantProcessed, processed, sortTaskOpt, cmp.AllowUnexported(Task{})); diff != "" {
 			t.Errorf("mismatch found in processed tasks; (-want, +got)\n%s", diff)
 		}
 		mu.Unlock()
@@ -592,7 +596,7 @@ func TestProcessorWithStrictPriority(t *testing.T) {
 		}
 		p.terminate()
 
-		if diff := cmp.Diff(tc.wantProcessed, processed, cmp.AllowUnexported(Payload{})); diff != "" {
+		if diff := cmp.Diff(tc.wantProcessed, processed, sortTaskOpt, cmp.AllowUnexported(Task{})); diff != "" {
 			t.Errorf("mismatch found in processed tasks; (-want, +got)\n%s", diff)
 		}
 
@@ -611,7 +615,7 @@ func TestProcessorPerform(t *testing.T) {
 			handler: func(ctx context.Context, t *Task) error {
 				return nil
 			},
-			task:    NewTask("gen_thumbnail", map[string]interface{}{"src": "some/img/path"}),
+			task:    NewTask("gen_thumbnail", h.JSON(map[string]interface{}{"src": "some/img/path"})),
 			wantErr: false,
 		},
 		{
@@ -619,7 +623,7 @@ func TestProcessorPerform(t *testing.T) {
 			handler: func(ctx context.Context, t *Task) error {
 				return fmt.Errorf("something went wrong")
 			},
-			task:    NewTask("gen_thumbnail", map[string]interface{}{"src": "some/img/path"}),
+			task:    NewTask("gen_thumbnail", h.JSON(map[string]interface{}{"src": "some/img/path"})),
 			wantErr: true,
 		},
 		{
@@ -627,7 +631,7 @@ func TestProcessorPerform(t *testing.T) {
 			handler: func(ctx context.Context, t *Task) error {
 				panic("something went terribly wrong")
 			},
-			task:    NewTask("gen_thumbnail", map[string]interface{}{"src": "some/img/path"}),
+			task:    NewTask("gen_thumbnail", h.JSON(map[string]interface{}{"src": "some/img/path"})),
 			wantErr: true,
 		},
 	}
diff --git a/scheduler.go b/scheduler.go
index 8daa507..21280d6 100644
--- a/scheduler.go
+++ b/scheduler.go
@@ -240,8 +240,8 @@ func (s *Scheduler) beat() {
 		e := &base.SchedulerEntry{
 			ID:      job.id.String(),
 			Spec:    job.cronspec,
-			Type:    job.task.Type,
-			Payload: job.task.Payload.data,
+			Type:    job.task.Type(),
+			Payload: job.task.Payload(),
 			Opts:    stringifyOptions(job.opts),
 			Next:    entry.Next,
 			Prev:    entry.Prev,
diff --git a/servemux.go b/servemux.go
index 4ccd6f6..6dc670d 100644
--- a/servemux.go
+++ b/servemux.go
@@ -62,7 +62,7 @@ func (mux *ServeMux) Handler(t *Task) (h Handler, pattern string) {
 	mux.mu.RLock()
 	defer mux.mu.RUnlock()
 
-	h, pattern = mux.match(t.Type)
+	h, pattern = mux.match(t.Type())
 	if h == nil {
 		h, pattern = NotFoundHandler(), ""
 	}
@@ -151,7 +151,7 @@ func (mux *ServeMux) Use(mws ...MiddlewareFunc) {
 
 // NotFound returns an error indicating that the handler was not found for the given task.
 func NotFound(ctx context.Context, task *Task) error {
-	return fmt.Errorf("handler not found for task %q", task.Type)
+	return fmt.Errorf("handler not found for task %q", task.Type())
 }
 
 // NotFoundHandler returns a simple task handler that returns a ``not found`` error.
diff --git a/servemux_test.go b/servemux_test.go
index 98dd52f..227c4d7 100644
--- a/servemux_test.go
+++ b/servemux_test.go
@@ -68,7 +68,7 @@ func TestServeMux(t *testing.T) {
 		}
 
 		if called != tc.want {
-			t.Errorf("%q handler was called for task %q, want %q to be called", called, task.Type, tc.want)
+			t.Errorf("%q handler was called for task %q, want %q to be called", called, task.Type(), tc.want)
 		}
 	}
 }
@@ -124,7 +124,7 @@ func TestServeMuxNotFound(t *testing.T) {
 		task := NewTask(tc.typename, nil)
 		err := mux.ProcessTask(context.Background(), task)
 		if err == nil {
-			t.Errorf("ProcessTask did not return error for task %q, should return 'not found' error", task.Type)
+			t.Errorf("ProcessTask did not return error for task %q, should return 'not found' error", task.Type())
 		}
 	}
 }
@@ -164,7 +164,7 @@ func TestServeMuxMiddlewares(t *testing.T) {
 		}
 
 		if called != tc.want {
-			t.Errorf("%q handler was called for task %q, want %q to be called", called, task.Type, tc.want)
+			t.Errorf("%q handler was called for task %q, want %q to be called", called, task.Type(), tc.want)
 		}
 	}
 }
diff --git a/server_test.go b/server_test.go
index 0343ada..6d29dd6 100644
--- a/server_test.go
+++ b/server_test.go
@@ -11,6 +11,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/hibiken/asynq/internal/asynqtest"
 	"github.com/hibiken/asynq/internal/rdb"
 	"github.com/hibiken/asynq/internal/testbroker"
 	"go.uber.org/goleak"
@@ -39,12 +40,12 @@ func TestServer(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	_, err = c.Enqueue(NewTask("send_email", map[string]interface{}{"recipient_id": 123}))
+	_, err = c.Enqueue(NewTask("send_email", asynqtest.JSON(map[string]interface{}{"recipient_id": 123})))
 	if err != nil {
 		t.Errorf("could not enqueue a task: %v", err)
 	}
 
-	_, err = c.Enqueue(NewTask("send_email", map[string]interface{}{"recipient_id": 456}), ProcessIn(1*time.Hour))
+	_, err = c.Enqueue(NewTask("send_email", asynqtest.JSON(map[string]interface{}{"recipient_id": 456})), ProcessIn(1*time.Hour))
 	if err != nil {
 		t.Errorf("could not enqueue a task: %v", err)
 	}
@@ -169,8 +170,8 @@ func TestServerWithFlakyBroker(t *testing.T) {
 
 	h := func(ctx context.Context, task *Task) error {
 		// force task retry.
-		if task.Type == "bad_task" {
-			return fmt.Errorf("could not process %q", task.Type)
+		if task.Type() == "bad_task" {
+			return fmt.Errorf("could not process %q", task.Type())
 		}
 		time.Sleep(2 * time.Second)
 		return nil