diff --git a/block/blk-tag.c b/block/blk-tag.c
index cc345e1d8d4e..3f33d8672268 100644
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -348,9 +348,16 @@ int blk_queue_start_tag(struct request_queue *q, struct request *rq)
 	 */
 	max_depth = bqt->max_depth;
 	if (!rq_is_sync(rq) && max_depth > 1) {
-		max_depth -= 2;
-		if (!max_depth)
+		switch (max_depth) {
+		case 2:
 			max_depth = 1;
+			break;
+		case 3:
+			max_depth = 2;
+			break;
+		default:
+			max_depth -= 2;
+		}
 		if (q->in_flight[BLK_RW_ASYNC] > max_depth)
 			return 1;
 	}