diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index af419af9a0f4a..c45d09a9a9421 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -1945,6 +1945,11 @@ static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
 
 static int null_validate_conf(struct nullb_device *dev)
 {
+	if (dev->queue_mode == NULL_Q_RQ) {
+		pr_err("legacy IO path is no longer available\n");
+		return -EINVAL;
+	}
+
 	dev->blocksize = round_down(dev->blocksize, 512);
 	dev->blocksize = clamp_t(unsigned int, dev->blocksize, 512, 4096);