diff --git a/src/io/io.go b/src/io/io.go
index 7c3539ac881..9cc3086c19b 100644
--- a/src/io/io.go
+++ b/src/io/io.go
@@ -369,7 +369,7 @@ func Copy(dst Writer, src Reader) (written int64, err error) {
 // temporary one. If buf is nil, one is allocated; otherwise if it has
 // zero length, CopyBuffer panics.
 //
-// If either src implements WriterTo or if dst implements ReaderFrom,
+// If either src implements WriterTo or dst implements ReaderFrom,
 // buf will not be used to perform the copy.
 func CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {
 	if buf != nil && len(buf) == 0 {