listen.go | 2 +-

diff --git a/listen.go b/listen.go
index 29015c100aa2e20d812a47b5a81e68cc910526b6..3840cc145a72b911438027847af806ada4ac046c 100644
--- a/listen.go
+++ b/listen.go
@@ -3,7 +3,7 @@
 import "strings"
 
 func LoopbackListenHost(network string) string {
-	if strings.Contains(network, "4") {
+	if strings.IndexByte(network, '4') != -1 {
 		return "127.0.0.1"
 	} else {
 		return "::1"