diff --git a/src/io/multi_test.go b/src/io/multi_test.go
index 909b6d8be2..c3a44fd3b2 100644
--- a/src/io/multi_test.go
+++ b/src/io/multi_test.go
@@ -141,7 +141,7 @@ func testMultiWriter(t *testing.T, sink interface {
 	}
 }
 
-// writerFunc is an Writer implemented by the underlying func.
+// writerFunc is a Writer implemented by the underlying func.
 type writerFunc func(p []byte) (int, error)
 
 func (f writerFunc) Write(p []byte) (int, error) {