diff -ruN cups-1.4.3/backend/usb-libusb.c cups-1.4.3-new/backend/usb-libusb.c
--- cups-1.4.3/backend/usb-libusb.c	2009-09-11 22:03:31.000000000 +0200
+++ cups-1.4.3-new/backend/usb-libusb.c	2010-05-25 18:25:52.000000000 +0200
@@ -518,10 +518,12 @@
 
   if ((sern = cupsGetOption("SERIALNUMBER", num_values, values)) == NULL)
     if ((sern = cupsGetOption("SERN", num_values, values)) == NULL)
-      if ((sern = cupsGetOption("SN", num_values, values)) == NULL)
+      if (((sern = cupsGetOption("SN", num_values, values)) == NULL) &&
+		(printer->device->descriptor.iSerialNumber != 0))
       {
        /*
-        * Try getting the serial number from the device itself...
+        * Try getting the serial number from the device itself,
+	* if it is available...
 	*/
 
         int length = usb_get_string_simple(printer->handle,