diff --git a/listen.go b/listen.go
index 29015c10..3840cc14 100644
--- a/listen.go
+++ b/listen.go
@@ -3,7 +3,7 @@ package torrent
 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"