diff --git a/servemux.go b/servemux.go
index 411dcf8..26bbf44 100644
--- a/servemux.go
+++ b/servemux.go
@@ -6,12 +6,16 @@ package asynq
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"sort"
 	"strings"
 	"sync"
 )
 
+// ErrHandlerNotFound indicates that no task handler was found for a given pattern.
+var ErrHandlerNotFound = errors.New("handler not found for task")
+
 // ServeMux is a multiplexer for asynchronous tasks.
 // It matches the type of each task against a list of registered patterns
 // and calls the handler for the pattern that most closely matches the
@@ -149,7 +153,7 @@ 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("%w %q", ErrHandlerNotFound, task.Type())
 }
 
 // NotFoundHandler returns a simple task handler that returns a ``not found`` error.