diff --git a/paho/client.go b/paho/client.go
index ad54e9c..5dcbeb2 100644
--- a/paho/client.go
+++ b/paho/client.go
@@ -399,10 +399,10 @@ func (c *Client) routePublishPackets() {
 // Disconnect, the Stop channel is closed or there is an error reading
 // a packet from the network connection
 func (c *Client) incoming() {
+	defer c.debug.Println("client stopping, incoming stopping")
 	for {
 		select {
 		case <-c.stop:
-			c.debug.Println("client stopping, incoming stopping")
 			return
 		default:
 			recv, err := packets.ReadPacket(c.Conn)
@@ -436,7 +436,15 @@ func (c *Client) incoming() {
 			case packets.PUBLISH:
 				pb := recv.Content.(*packets.Publish)
 				c.debug.Printf("received QoS%d PUBLISH", pb.QoS)
-				c.publishPackets <- pb
+				c.mu.Lock()
+				select {
+				case <-c.stop:
+					c.mu.Unlock()
+					return
+				default:
+					c.publishPackets <- pb
+					c.mu.Unlock()
+				}
 			case packets.PUBACK, packets.PUBCOMP, packets.SUBACK, packets.UNSUBACK:
 				c.debug.Printf("received %s packet with id %d", recv.PacketType(), recv.PacketID())
 				if cpCtx := c.MIDs.Get(recv.PacketID()); cpCtx != nil {
@@ -550,12 +558,18 @@ func (c *Client) error(e error) {
 // is received.
 func (c *Client) Authenticate(ctx context.Context, a *Auth) (*AuthResponse, error) {
 	c.debug.Println("client initiated reauthentication")
-	c.mu.Lock()
-	defer c.mu.Unlock()
 
+	c.mu.Lock()
+	if c.raCtx != nil {
+		c.mu.Unlock()
+		return nil, fmt.Errorf("previous authentication is still in progress")
+	}
 	c.raCtx = &CPContext{ctx, make(chan packets.ControlPacket, 1)}
+	c.mu.Unlock()
 	defer func() {
+		c.mu.Lock()
 		c.raCtx = nil
+		c.mu.Unlock()
 	}()
 
 	c.debug.Println("sending AUTH")
diff --git a/paho/client_test.go b/paho/client_test.go
index fd50c9c..3796ca2 100644
--- a/paho/client_test.go
+++ b/paho/client_test.go
@@ -750,6 +750,63 @@ func TestCloseDeadlock(t *testing.T) {
 	wg.Wait()
 }
 
+func TestSendOnClosedChannel(t *testing.T) {
+	ts := newTestServer()
+	ts.SetResponse(packets.CONNACK, &packets.Connack{
+		ReasonCode:     0,
+		SessionPresent: false,
+		Properties: &packets.Properties{
+			MaximumPacketSize: Uint32(12345),
+			MaximumQOS:        Byte(1),
+			ReceiveMaximum:    Uint16(12345),
+			TopicAliasMaximum: Uint16(200),
+		},
+	})
+	go ts.Run()
+	defer ts.Stop()
+
+	c := NewClient(ClientConfig{
+		Conn: ts.ClientConn(),
+	})
+	require.NotNil(t, c)
+
+	if testing.Verbose() {
+		l := log.New(os.Stdout, t.Name(), log.LstdFlags)
+		c.SetDebugLogger(l)
+		c.SetErrorLogger(l)
+	}
+
+	ctx := context.Background()
+	ca, err := c.Connect(ctx, &Connect{
+		KeepAlive:  30,
+		ClientID:   "testClient",
+		CleanStart: true,
+		Properties: &ConnectProperties{
+			ReceiveMaximum: Uint16(200),
+		},
+	})
+	require.Nil(t, err)
+	assert.Equal(t, uint8(0), ca.ReasonCode)
+
+	go func() {
+		for i := uint16(0); true; i++ {
+			err := ts.SendPacket(&packets.Publish{
+				Payload:  []byte("ciao"),
+				Topic:    "test",
+				PacketID: i,
+				QoS:      1,
+			})
+			if err != nil {
+				t.Logf("Send packet error: %v", err)
+				return
+			}
+		}
+	}()
+
+	time.Sleep(10 * time.Millisecond)
+	c.close()
+}
+
 func isChannelClosed(ch chan struct{}) (closed bool) {
 	defer func() {
 		err, ok := recover().(error)