Index: umass.c
===================================================================
--- umass.c	(revision 196776)
+++ umass.c	(working copy)
@@ -124,6 +124,7 @@ __FBSDID("$FreeBSD$");
 
 #include <dev/usb/usb.h>
 #include <dev/usb/usbdi.h>
+#include <dev/usb/usb_device.h>
 #include "usbdevs.h"
 
 #include <cam/cam.h>
@@ -2978,6 +2979,25 @@ umass_cam_action(struct cam_sim *sim, union ccb *c
 				if (sc->sc_transfer.cmd_data[0] == INQUIRY) {
 
 					/*
+					 * Umass devices don't generally report their serial numbers
+					 * in the usual SCSI way.  Emulate it here.
+					 */
+					if (sc->sc_transfer.cmd_data[1] & SI_EVPD &&
+					    sc->sc_transfer.cmd_data[2] == 0x80) {
+						struct scsi_vpd_unit_serial_number *vpd_serial;
+
+						vpd_serial = (struct scsi_vpd_unit_serial_number *)ccb->csio.data_ptr;
+						vpd_serial->length = strlen(sc->sc_udev->serial);
+						if (vpd_serial->length > sizeof(vpd_serial->serial_num))
+							vpd_serial->length = sizeof(vpd_serial->serial_num);
+						memcpy(vpd_serial->serial_num, sc->sc_udev->serial, vpd_serial->length);
+						ccb->csio.scsi_status = SCSI_STATUS_OK;
+						ccb->ccb_h.status = CAM_REQ_CMP;
+						xpt_done(ccb);
+						goto done;
+					}
+
+					/*
 					 * Handle EVPD inquiry for broken devices first
 					 * NO_INQUIRY also implies NO_INQUIRY_EVPD
 					 */