diff --git a/drivers/usb/serial/mos7720.c b/drivers/usb/serial/mos7720.c
index 725991f..40f3a01 100644
--- a/drivers/usb/serial/mos7720.c
+++ b/drivers/usb/serial/mos7720.c
@@ -564,22 +564,25 @@
 	}
 
 	/* While closing port, shutdown all bulk read, write  *
-	 * and interrupt read if they exists                  */
-	if (serial->dev) {
-		dbg("Shutdown bulk write");
-		usb_kill_urb(port->write_urb);
-		dbg("Shutdown bulk read");
-		usb_kill_urb(port->read_urb);
+	 * and interrupt read if they exists, otherwise nop   */
+	dbg("Shutdown bulk write");
+	usb_kill_urb(port->write_urb);
+	dbg("Shutdown bulk read");
+	usb_kill_urb(port->read_urb);
+
+	mutex_lock(&serial->disc_mutex);
+	/* these commands must not be issued if the device has
+	 * been disconnected */
+	if (!serial->disconnected) {
+		data = 0x00;
+		send_mos_cmd(serial, MOS_WRITE, port->number - port->serial->minor,
+			     0x04, &data);
+
+		data = 0x00;
+		send_mos_cmd(serial, MOS_WRITE, port->number - port->serial->minor,
+			     0x01, &data);
 	}
-
-	data = 0x00;
-	send_mos_cmd(serial, MOS_WRITE, port->number - port->serial->minor,
-		     0x04, &data);
-
-	data = 0x00;
-	send_mos_cmd(serial, MOS_WRITE, port->number - port->serial->minor,
-		     0x01, &data);
-
+	mutex_unlock(&serial->disc_mutex);
 	mos7720_port->open = 0;
 
 	dbg("Leaving %s", __FUNCTION__);
diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 28315b0..3ce98e8 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -634,6 +634,7 @@
 	serial->type = driver;
 	serial->interface = interface;
 	kref_init(&serial->kref);
+	mutex_init(&serial->disc_mutex);
 
 	return serial;
 }
@@ -1089,20 +1090,22 @@
 	usb_serial_console_disconnect(serial);
 	dbg ("%s", __FUNCTION__);
 
+	mutex_lock(&serial->disc_mutex);
 	usb_set_intfdata (interface, NULL);
-	if (serial) {
-		for (i = 0; i < serial->num_ports; ++i) {
-			port = serial->port[i];
-			if (port) {
-				if (port->tty)
-					tty_hangup(port->tty);
-				kill_traffic(port);
-			}
+	/* must set a flag, to signal subdrivers */
+	serial->disconnected = 1;
+	for (i = 0; i < serial->num_ports; ++i) {
+		port = serial->port[i];
+		if (port) {
+			if (port->tty)
+				tty_hangup(port->tty);
+			kill_traffic(port);
 		}
-		/* let the last holder of this object 
-		 * cause it to be cleaned up */
-		usb_serial_put(serial);
 	}
+	/* let the last holder of this object
+	 * cause it to be cleaned up */
+	mutex_unlock(&serial->disc_mutex);
+	usb_serial_put(serial);
 	dev_info(dev, "device disconnected\n");
 }
 
@@ -1112,9 +1115,6 @@
 	struct usb_serial_port *port;
 	int i, r = 0;
 
-	if (!serial) /* device has been disconnected */
-		return 0;
-
 	for (i = 0; i < serial->num_ports; ++i) {
 		port = serial->port[i];
 		if (port)
diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index ef1e430..63b29b5 100644
--- a/include/linux/usb/serial.h
+++ b/include/linux/usb/serial.h
@@ -129,6 +129,7 @@
 	struct usb_device *		dev;
 	struct usb_serial_driver *	type;
 	struct usb_interface *		interface;
+	unsigned char			disconnected;
 	unsigned char			minor;
 	unsigned char			num_ports;
 	unsigned char			num_port_pointers;
@@ -138,6 +139,7 @@
 	char				num_bulk_out;
 	struct usb_serial_port *	port[MAX_NUM_PORTS];
 	struct kref			kref;
+	struct mutex			disc_mutex;
 	void *				private;
 };
 #define to_usb_serial(d) container_of(d, struct usb_serial, kref)