diff --git a/src/pkg/testing/iotest/reader.go b/src/pkg/testing/iotest/reader.go
index ab8dc31a1f..441b9102d9 100644
--- a/src/pkg/testing/iotest/reader.go
+++ b/src/pkg/testing/iotest/reader.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package iotest implements Readers and Writers useful only for testing.
+// Package iotest implements Readers and Writers useful mainly for testing.
 package iotest
 
 import (