diff --git a/pkg/core/track.go b/pkg/core/track.go
index 8bc65374..d3f1467d 100644
--- a/pkg/core/track.go
+++ b/pkg/core/track.go
@@ -140,6 +140,7 @@ func (s *Sender) Start() {
 	s.done = make(chan struct{})
 
 	go func() {
+		// for range on nil chan is OK
 		for packet := range s.buf {
 			s.Output(packet)
 		}
@@ -148,7 +149,7 @@ func (s *Sender) Start() {
 }
 
 func (s *Sender) Wait() {
-	if done := s.done; s.done != nil {
+	if done := s.done; done != nil {
 		<-done
 	}
 }
@@ -165,10 +166,12 @@ func (s *Sender) State() string {
 
 func (s *Sender) Close() {
 	// close buffer if exists
-	if buf := s.buf; buf != nil {
-		s.buf = nil
-		defer close(buf)
+	s.mu.Lock()
+	if s.buf != nil {
+		close(s.buf) // exit from for range loop
+		s.buf = nil  // prevent writing to closed chan
 	}
+	s.mu.Unlock()
 
 	s.Node.Close()
 }
diff --git a/pkg/core/track_test.go b/pkg/core/track_test.go
new file mode 100644
index 00000000..cf877d49
--- /dev/null
+++ b/pkg/core/track_test.go
@@ -0,0 +1,53 @@
+package core
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSenser(t *testing.T) {
+	recv := make(chan *Packet) // blocking receiver
+
+	sender := NewSender(nil, &Codec{})
+	sender.Output = func(packet *Packet) {
+		recv <- packet
+	}
+	require.Equal(t, "new", sender.State())
+
+	sender.Start()
+	require.Equal(t, "connected", sender.State())
+
+	sender.Input(&Packet{})
+	sender.Input(&Packet{})
+
+	require.Equal(t, 2, sender.Packets)
+	require.Equal(t, 0, sender.Drops)
+
+	// important to read one before close
+	// because goroutine in Start() can run with nil chan
+	// it's OK in real life, but bad for test
+	_, ok := <-recv
+	require.True(t, ok)
+
+	sender.Close()
+	require.Equal(t, "closed", sender.State())
+
+	sender.Input(&Packet{})
+
+	require.Equal(t, 2, sender.Packets)
+	require.Equal(t, 1, sender.Drops)
+
+	// read 2nd
+	_, ok = <-recv
+	require.True(t, ok)
+
+	// read 3rd
+	select {
+	case <-recv:
+		ok = true
+	default:
+		ok = false
+	}
+	require.False(t, ok)
+}