diff --git a/src/bytes/buffer.go b/src/bytes/buffer.go
index 67771846fc4..dc9d5e95d32 100644
--- a/src/bytes/buffer.go
+++ b/src/bytes/buffer.go
@@ -56,6 +56,8 @@ func (b *Buffer) Bytes() []byte { return b.buf[b.off:] }
 
 // String returns the contents of the unread portion of the buffer
 // as a string. If the Buffer is a nil pointer, it returns "<nil>".
+//
+// To build strings more efficiently, see the strings.Builder type.
 func (b *Buffer) String() string {
 	if b == nil {
 		// Special case, useful in debugging.