--- a/drivers/usb/serial/mos7720.c	2007-03-06 16:16:16.000000000 +0100
+++ b/drivers/usb/serial/mos7720.c	2007-03-06 16:16:21.000000000 +0100
@@ -334,7 +334,7 @@
 	int port_number;
 	char data;
 	int j;
-
+BUG_ON(port == NULL);
 	serial = port->serial;
 
 	mos7720_port = usb_get_serial_port_data(port);