diff --git a/src/cli/cli.go b/src/cli/cli.go
index 6695f95..b9daf87 100644
--- a/src/cli/cli.go
+++ b/src/cli/cli.go
@@ -79,6 +79,7 @@ func Run() (err error) {
 			HelpName:    "croc relay",
 			Action:      relay,
 			Flags: []cli.Flag{
+				&cli.StringFlag{Name: "host", Usage: "host of the relay"},
 				&cli.StringFlag{Name: "ports", Value: "9009,9010,9011,9012,9013", Usage: "ports of the relay"},
 			},
 		},
@@ -526,6 +527,7 @@ func relay(c *cli.Context) (err error) {
 	if c.Bool("debug") {
 		debugString = "debug"
 	}
+	host := c.String("host")
 	ports := strings.Split(c.String("ports"), ",")
 	tcpPorts := strings.Join(ports[1:], ",")
 	for i, port := range ports {
@@ -533,11 +535,11 @@ func relay(c *cli.Context) (err error) {
 			continue
 		}
 		go func(portStr string) {
-			err = tcp.Run(debugString, portStr, determinePass(c))
+			err = tcp.Run(debugString, host, portStr, determinePass(c))
 			if err != nil {
 				panic(err)
 			}
 		}(port)
 	}
-	return tcp.Run(debugString, ports[0], determinePass(c), tcpPorts)
+	return tcp.Run(debugString, host, ports[0], determinePass(c), tcpPorts)
 }
diff --git a/src/croc/croc.go b/src/croc/croc.go
index acd562d..93c6e18 100644
--- a/src/croc/croc.go
+++ b/src/croc/croc.go
@@ -296,7 +296,7 @@ func (c *Client) setupLocalRelay() {
 			if c.Options.Debug {
 				debugString = "debug"
 			}
-			err := tcp.Run(debugString, portStr, c.Options.RelayPassword, strings.Join(c.Options.RelayPorts[1:], ","))
+			err := tcp.Run(debugString, "localhost", portStr, c.Options.RelayPassword, strings.Join(c.Options.RelayPorts[1:], ","))
 			if err != nil {
 				panic(err)
 			}
diff --git a/src/croc/croc_test.go b/src/croc/croc_test.go
index 4142764..afd53ab 100644
--- a/src/croc/croc_test.go
+++ b/src/croc/croc_test.go
@@ -15,11 +15,11 @@ import (
 func init() {
 	log.SetLevel("trace")
 
-	go tcp.Run("debug", "8081", "pass123", "8082,8083,8084,8085")
-	go tcp.Run("debug", "8082", "pass123")
-	go tcp.Run("debug", "8083", "pass123")
-	go tcp.Run("debug", "8084", "pass123")
-	go tcp.Run("debug", "8085", "pass123")
+	go tcp.Run("debug", "localhost", "8081", "pass123", "8082,8083,8084,8085")
+	go tcp.Run("debug", "localhost", "8082", "pass123")
+	go tcp.Run("debug", "localhost", "8083", "pass123")
+	go tcp.Run("debug", "localhost", "8084", "pass123")
+	go tcp.Run("debug", "localhost", "8085", "pass123")
 	time.Sleep(1 * time.Second)
 }
 
diff --git a/src/tcp/tcp.go b/src/tcp/tcp.go
index c57baf3..d7b3c3b 100644
--- a/src/tcp/tcp.go
+++ b/src/tcp/tcp.go
@@ -17,6 +17,7 @@ import (
 )
 
 type server struct {
+	host       string
 	port       string
 	debugLevel string
 	banner     string
@@ -42,8 +43,9 @@ const (
 )
 
 // Run starts a tcp listener, run async
-func Run(debugLevel, port, password string, banner ...string) (err error) {
+func Run(debugLevel, host, port, password string, banner ...string) (err error) {
 	s := new(server)
+	s.host = host
 	s.port = port
 	s.password = password
 	s.debugLevel = debugLevel
@@ -87,10 +89,30 @@ func (s *server) start() (err error) {
 }
 
 func (s *server) run() (err error) {
-	log.Infof("starting TCP server on " + s.port)
-	server, err := net.Listen("tcp", ":"+s.port)
+	network := "tcp"
+	addr := net.JoinHostPort(s.host, s.port)
+	if s.host != "" {
+		ip := net.ParseIP(s.host)
+		if ip == nil {
+			tcpIP, err := net.ResolveIPAddr("ip", s.host)
+			if err != nil {
+				return err
+			}
+			ip = tcpIP.IP
+		}
+		addr = net.JoinHostPort(ip.String(), s.port)
+		if s.host != "" {
+			if ip.To4() != nil {
+				network = "tcp4"
+			} else {
+				network = "tcp6"
+			}
+		}
+	}
+	log.Infof("starting TCP server on " + addr)
+	server, err := net.Listen(network, addr)
 	if err != nil {
-		return fmt.Errorf("error listening on %s: %w", s.port, err)
+		return fmt.Errorf("error listening on %s: %w", addr, err)
 	}
 	defer server.Close()
 	// spawn a new goroutine whenever a client connects
diff --git a/src/tcp/tcp_test.go b/src/tcp/tcp_test.go
index ccceba7..165f953 100644
--- a/src/tcp/tcp_test.go
+++ b/src/tcp/tcp_test.go
@@ -12,7 +12,7 @@ import (
 
 func BenchmarkConnection(b *testing.B) {
 	log.SetLevel("trace")
-	go Run("debug", "8283", "pass123", "8284")
+	go Run("debug", "localhost", "8283", "pass123", "8284")
 	time.Sleep(100 * time.Millisecond)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -24,7 +24,7 @@ func BenchmarkConnection(b *testing.B) {
 func TestTCP(t *testing.T) {
 	log.SetLevel("error")
 	timeToRoomDeletion = 100 * time.Millisecond
-	go Run("debug", "8281", "pass123", "8282")
+	go Run("debug", "localhost", "8281", "pass123", "8282")
 	time.Sleep(100 * time.Millisecond)
 	err := PingServer("localhost:8281")
 	assert.Nil(t, err)