diff --git a/aggregator.go b/aggregator.go
index d4a5680..7340f3c 100644
--- a/aggregator.go
+++ b/aggregator.go
@@ -31,8 +31,8 @@ type aggregator struct {
 	maxDelay    time.Duration
 	maxSize     int
 
-	// Aggregation function
-	aggregateFunc func(gname string, tasks []*Task) *Task
+	// User provided group aggregator.
+	ga GroupAggregator
 
 	// interval used to check for aggregation
 	interval time.Duration
@@ -43,13 +43,13 @@ type aggregator struct {
 }
 
 type aggregatorParams struct {
-	logger        *log.Logger
-	broker        base.Broker
-	queues        []string
-	gracePeriod   time.Duration
-	maxDelay      time.Duration
-	maxSize       int
-	aggregateFunc func(gname string, msgs []*Task) *Task
+	logger          *log.Logger
+	broker          base.Broker
+	queues          []string
+	gracePeriod     time.Duration
+	maxDelay        time.Duration
+	maxSize         int
+	groupAggregator GroupAggregator
 }
 
 const (
@@ -67,22 +67,22 @@ func newAggregator(params aggregatorParams) *aggregator {
 		interval = params.gracePeriod
 	}
 	return &aggregator{
-		logger:        params.logger,
-		broker:        params.broker,
-		client:        &Client{broker: params.broker},
-		done:          make(chan struct{}),
-		queues:        params.queues,
-		gracePeriod:   params.gracePeriod,
-		maxDelay:      params.maxDelay,
-		maxSize:       params.maxSize,
-		aggregateFunc: params.aggregateFunc,
-		sema:          make(chan struct{}, maxConcurrentAggregationChecks),
-		interval:      interval,
+		logger:      params.logger,
+		broker:      params.broker,
+		client:      &Client{broker: params.broker},
+		done:        make(chan struct{}),
+		queues:      params.queues,
+		gracePeriod: params.gracePeriod,
+		maxDelay:    params.maxDelay,
+		maxSize:     params.maxSize,
+		ga:          params.groupAggregator,
+		sema:        make(chan struct{}, maxConcurrentAggregationChecks),
+		interval:    interval,
 	}
 }
 
 func (a *aggregator) shutdown() {
-	if a.aggregateFunc == nil {
+	if a.ga == nil {
 		return
 	}
 	a.logger.Debug("Aggregator shutting down...")
@@ -91,7 +91,7 @@ func (a *aggregator) shutdown() {
 }
 
 func (a *aggregator) start(wg *sync.WaitGroup) {
-	if a.aggregateFunc == nil {
+	if a.ga == nil {
 		return
 	}
 	wg.Add(1)
@@ -158,7 +158,7 @@ func (a *aggregator) aggregate(t time.Time) {
 			for i, m := range msgs {
 				tasks[i] = NewTask(m.Type, m.Payload)
 			}
-			aggregatedTask := a.aggregateFunc(gname, tasks)
+			aggregatedTask := a.ga.Aggregate(gname, tasks)
 			ctx, cancel := context.WithDeadline(context.Background(), deadline)
 			if _, err := a.client.EnqueueContext(ctx, aggregatedTask); err != nil {
 				a.logger.Errorf("Failed to enqueue aggregated task (queue=%q, group=%q, setID=%q): %v",
diff --git a/aggregator_test.go b/aggregator_test.go
index d46d639..ccce306 100644
--- a/aggregator_test.go
+++ b/aggregator_test.go
@@ -120,13 +120,13 @@ func TestAggregator(t *testing.T) {
 		h.FlushDB(t, r)
 
 		aggregator := newAggregator(aggregatorParams{
-			logger:        testLogger,
-			broker:        rdbClient,
-			queues:        []string{"default"},
-			gracePeriod:   tc.gracePeriod,
-			maxDelay:      tc.maxDelay,
-			maxSize:       tc.maxSize,
-			aggregateFunc: tc.aggregateFunc,
+			logger:          testLogger,
+			broker:          rdbClient,
+			queues:          []string{"default"},
+			gracePeriod:     tc.gracePeriod,
+			maxDelay:        tc.maxDelay,
+			maxSize:         tc.maxSize,
+			groupAggregator: GroupAggregatorFunc(tc.aggregateFunc),
 		})
 
 		var wg sync.WaitGroup
diff --git a/server.go b/server.go
index ad6d7e3..945a7c3 100644
--- a/server.go
+++ b/server.go
@@ -216,10 +216,26 @@ type Config struct {
 	// If unset or zero, no size limit is used.
 	GroupMaxSize int
 
-	// GroupAggregateFunc specifies the aggregation function used to aggregate multiple tasks in a group into one task.
+	// GroupAggregator specifies the aggregation function used to aggregate multiple tasks in a group into one task.
 	//
 	// If unset or nil, the group aggregation feature will be disabled on the server.
-	GroupAggregateFunc func(groupKey string, tasks []*Task) *Task
+	GroupAggregator GroupAggregator
+}
+
+// GroupAggregator aggregates a group of tasks into one before the tasks are passed to the Handler.
+type GroupAggregator interface {
+	// Aggregate aggregates the given tasks which belong to a same group
+	// and returns a new task which is the aggregation of those tasks.
+	Aggregate(groupKey string, tasks []*Task) *Task
+}
+
+// The GroupAggregatorFunc type is an adapter to allow the use of  ordinary functions as a GroupAggregator.
+// If f is a function with the appropriate signature, GroupAggregatorFunc(f) is a GroupAggregator that calls f.
+type GroupAggregatorFunc func(groupKey string, tasks []*Task) *Task
+
+// Aggregate calls fn(groupKey, tasks)
+func (fn GroupAggregatorFunc) Aggregate(groupKey string, tasks []*Task) *Task {
+	return fn(groupKey, tasks)
 }
 
 // An ErrorHandler handles an error occured during task processing.
@@ -506,13 +522,13 @@ func NewServer(r RedisConnOpt, cfg Config) *Server {
 		interval: 8 * time.Second,
 	})
 	aggregator := newAggregator(aggregatorParams{
-		logger:        logger,
-		broker:        rdb,
-		queues:        qnames,
-		gracePeriod:   groupGracePeriod,
-		maxDelay:      cfg.GroupMaxDelay,
-		maxSize:       cfg.GroupMaxSize,
-		aggregateFunc: cfg.GroupAggregateFunc,
+		logger:          logger,
+		broker:          rdb,
+		queues:          qnames,
+		gracePeriod:     groupGracePeriod,
+		maxDelay:        cfg.GroupMaxDelay,
+		maxSize:         cfg.GroupMaxSize,
+		groupAggregator: cfg.GroupAggregator,
 	})
 	return &Server{
 		logger:        logger,