diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 0b09638fa39b..1f5d92a25a49 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -836,6 +836,7 @@ static int sd_setup_write_same_cmnd(struct scsi_cmnd *cmd)
 	struct bio *bio = rq->bio;
 	sector_t sector = blk_rq_pos(rq);
 	unsigned int nr_sectors = blk_rq_sectors(rq);
+	unsigned int nr_bytes = blk_rq_bytes(rq);
 	int ret;
 
 	if (sdkp->device->no_write_same)
@@ -868,7 +869,21 @@ static int sd_setup_write_same_cmnd(struct scsi_cmnd *cmd)
 
 	cmd->transfersize = sdp->sector_size;
 	cmd->allowed = SD_MAX_RETRIES;
-	return scsi_init_io(cmd);
+
+	/*
+	 * For WRITE SAME the data transferred via the DATA OUT buffer is
+	 * different from the amount of data actually written to the target.
+	 *
+	 * We set up __data_len to the amount of data transferred via the
+	 * DATA OUT buffer so that blk_rq_map_sg sets up the proper S/G list
+	 * to transfer a single sector of data first, but then reset it to
+	 * the amount of data to be written right after so that the I/O path
+	 * knows how much to actually write.
+	 */
+	rq->__data_len = sdp->sector_size;
+	ret = scsi_init_io(cmd);
+	rq->__data_len = nr_bytes;
+	return ret;
 }
 
 static int sd_setup_flush_cmnd(struct scsi_cmnd *cmd)