diff --git a/block/blk-core.c b/block/blk-core.c
index 1e3b97f..394c5bd 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2097,6 +2097,9 @@
 
 int __init blk_dev_init(void)
 {
+	BUILD_BUG_ON(__REQ_NR_BITS > 8 *
+			sizeof(((struct request *)0)->cmd_flags));
+
 	kblockd_workqueue = create_workqueue("kblockd");
 	if (!kblockd_workqueue)
 		panic("Failed to create kblockd\n");