diff --git a/adapter/outbound/util.go b/adapter/outbound/util.go
index de9287bd..0b859630 100644
--- a/adapter/outbound/util.go
+++ b/adapter/outbound/util.go
@@ -103,7 +103,8 @@ func resolveUDPAddrWithPrefer(network, address string, prefer C.DNSPrefer) (*net
 			}
 			ip = fallback
 		}
-	case C.IPv4Prefer | C.DualStack:
+	default:
+		// C.IPv4Prefer, C.DualStack and other 
 		var ips []netip.Addr
 		ips, err = resolver.ResolveAllIPProxyServerHost(host)
 		var fallback netip.Addr