diff --git a/forward.go b/forward.go
index 73e85b9..9e25fa3 100644
--- a/forward.go
+++ b/forward.go
@@ -361,6 +361,10 @@ func TCPRemoteForwardListener(addr string, chain *Chain) (Listener, error) {
 }
 
 func (l *tcpRemoteForwardListener) isChainValid() bool {
+	if l.chain.IsEmpty() {
+		return false
+	}
+
 	lastNode := l.chain.LastNode()
 	if (lastNode.Protocol == "forward" && lastNode.Transport == "ssh") ||
 		lastNode.Protocol == "socks5" || lastNode.Protocol == "" {
@@ -429,7 +433,7 @@ func (l *tcpRemoteForwardListener) accept() (conn net.Conn, err error) {
 		return l.chain.Dial(l.addr.String())
 	}
 
-	if lastNode.Protocol == "socks5" || lastNode.Protocol == "" {
+	if l.isChainValid() {
 		if lastNode.GetBool("mbind") {
 			return l.muxAccept() // multiplexing support for binding.
 		}
@@ -588,6 +592,8 @@ type udpRemoteForwardListener struct {
 	ln       *net.UDPConn
 	ttl      time.Duration
 	closed   chan struct{}
+	ready    chan struct{}
+	once     sync.Once
 	closeMux sync.Mutex
 	config   *UDPListenConfig
 }
@@ -613,18 +619,25 @@ func UDPRemoteForwardListener(addr string, chain *Chain, cfg *UDPListenConfig) (
 		chain:    chain,
 		connMap:  new(udpConnMap),
 		connChan: make(chan net.Conn, backlog),
+		ready:    make(chan struct{}),
 		closed:   make(chan struct{}),
 		config:   cfg,
 	}
 
 	go ln.listenLoop()
 
+	<-ln.ready
+
 	return ln, err
 }
 
 func (l *udpRemoteForwardListener) isChainValid() bool {
+	if l.chain.IsEmpty() {
+		return false
+	}
+
 	lastNode := l.chain.LastNode()
-	return lastNode.Protocol == "socks5"
+	return lastNode.Protocol == "socks5" || lastNode.Protocol == ""
 }
 
 func (l *udpRemoteForwardListener) listenLoop() {
@@ -635,6 +648,10 @@ func (l *udpRemoteForwardListener) listenLoop() {
 			return
 		}
 
+		l.once.Do(func() {
+			close(l.ready)
+		})
+
 		func() {
 			defer conn.Close()
 
@@ -691,8 +708,7 @@ func (l *udpRemoteForwardListener) connect() (conn net.PacketConn, err error) {
 		default:
 		}
 
-		lastNode := l.chain.LastNode()
-		if lastNode.Protocol == "socks5" || lastNode.Protocol == "" {
+		if l.isChainValid() {
 			var cc net.Conn
 			cc, err = getSocks5UDPTunnel(l.chain, l.addr)
 			if err != nil {