diff --git a/hw/usb-msd.c b/hw/usb-msd.c
index c3a197a..1064920 100644
--- a/hw/usb-msd.c
+++ b/hw/usb-msd.c
@@ -253,7 +253,7 @@
     s->scsi_buf = s->scsi_dev->info->get_buf(s->scsi_dev, tag);
     if (p) {
         usb_msd_copy_data(s);
-        if (s->usb_len == 0) {
+        if (s->packet && s->usb_len == 0) {
             /* Set s->packet to NULL before calling usb_packet_complete
                because another request may be issued before
                usb_packet_complete returns.  */