diff --git a/block/blk-flush.c b/block/blk-flush.c
index 491eb30a242db435b55a7ba962e4acce5af81a15..89ae3b9bf7ca7515eec7b36d5c71ba6501a26a53 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -320,7 +320,7 @@ void blk_insert_flush(struct request *rq)
 		return;
 	}
 
-	BUG_ON(!rq->bio || rq->bio != rq->biotail);
+	BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
 
 	/*
 	 * If there's data but flush is not necessary, the request can be