diff --git a/hw/usb/dev-storage.c b/hw/usb/dev-storage.c
index 924a86f964..5b9a286766 100644
--- a/hw/usb/dev-storage.c
+++ b/hw/usb/dev-storage.c
@@ -48,8 +48,8 @@ struct usb_msd_csw {
 typedef struct {
     USBDevice dev;
     enum USBMSDMode mode;
+    uint32_t scsi_off;
     uint32_t scsi_len;
-    uint8_t *scsi_buf;
     uint32_t data_len;
     struct usb_msd_csw csw;
     SCSIRequest *req;
@@ -178,9 +178,9 @@ static void usb_msd_copy_data(MSDState *s, USBPacket *p)
     len = p->iov.size - p->result;
     if (len > s->scsi_len)
         len = s->scsi_len;
-    usb_packet_copy(p, s->scsi_buf, len);
+    usb_packet_copy(p, scsi_req_get_buf(s->req) + s->scsi_off, len);
     s->scsi_len -= len;
-    s->scsi_buf += len;
+    s->scsi_off += len;
     s->data_len -= len;
     if (s->scsi_len == 0 || s->data_len == 0) {
         scsi_req_continue(s->req);
@@ -219,7 +219,7 @@ static void usb_msd_transfer_data(SCSIRequest *req, uint32_t len)
 
     assert((s->mode == USB_MSDM_DATAOUT) == (req->cmd.mode == SCSI_XFER_TO_DEV));
     s->scsi_len = len;
-    s->scsi_buf = scsi_req_get_buf(req);
+    s->scsi_off = 0;
     if (p) {
         usb_msd_copy_data(s, p);
         p = s->packet;