diff --git a/core/mr/mapreduce.go b/core/mr/mapreduce.go
index f563b5bf..70dd7a6d 100644
--- a/core/mr/mapreduce.go
+++ b/core/mr/mapreduce.go
@@ -16,7 +16,7 @@ const (
 	minWorkers     = 1
 )
 
-var ErrCancelWithNil = errors.New("mr cancelled with nil")
+var ErrCancelWithNil = errors.New("mapreduce cancelled with nil")
 
 type (
 	GenerateFunc    func(source chan<- interface{})