diff --git a/testing/scenarios/common.go b/testing/scenarios/common.go
index 290f467f..7044e689 100644
--- a/testing/scenarios/common.go
+++ b/testing/scenarios/common.go
@@ -30,6 +30,18 @@ func pickPort() v2net.Port {
 	return v2net.Port(addr.Port)
 }
 
+func pickUDPPort() v2net.Port {
+	conn, err := net.ListenUDP("udp4", &net.UDPAddr{
+		IP:   v2net.LocalHostIP.IP(),
+		Port: 0,
+	})
+	common.Must(err)
+	defer conn.Close()
+
+	addr := conn.LocalAddr().(*net.UDPAddr)
+	return v2net.Port(addr.Port)
+}
+
 func xor(b []byte) []byte {
 	r := make([]byte, len(b))
 	for i, v := range b {
diff --git a/testing/scenarios/vmess_test.go b/testing/scenarios/vmess_test.go
index 3fa82a7a..063fe683 100644
--- a/testing/scenarios/vmess_test.go
+++ b/testing/scenarios/vmess_test.go
@@ -1095,7 +1095,7 @@ func TestVMessGCMMuxUDP(t *testing.T) {
 	}
 
 	clientPort := pickPort()
-	clientUDPPort := pickPort()
+	clientUDPPort := pickUDPPort()
 	clientConfig := &core.Config{
 		Inbound: []*proxyman.InboundHandlerConfig{
 			{
@@ -1203,7 +1203,7 @@ func TestVMessGCMMuxUDP(t *testing.T) {
 				payload := make([]byte, 1024)
 				rand.Read(payload)
 
-				for j := 0; j < 10; j++ {
+				for j := 0; j < 5; j++ {
 					nBytes, _, err := conn.WriteMsgUDP(payload, nil, nil)
 					assert.Error(err).IsNil()
 					assert.Int(nBytes).Equals(len(payload))
@@ -1211,7 +1211,7 @@ func TestVMessGCMMuxUDP(t *testing.T) {
 
 				response := make([]byte, 1024)
 				oob := make([]byte, 16)
-				for j := 0; j < 10; j++ {
+				for j := 0; j < 5; j++ {
 					nBytes, _, _, _, err := conn.ReadMsgUDP(response, oob)
 					assert.Error(err).IsNil()
 					assert.Int(nBytes).Equals(1024)