diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index bf8148ebd858..bd05eaf04143 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1773,11 +1773,11 @@ static int nbd_dev_add(int index)
 	disk->major = NBD_MAJOR;
 
 	/* Too big first_minor can cause duplicate creation of
-	 * sysfs files/links, since first_minor will be truncated to
-	 * byte in __device_add_disk().
+	 * sysfs files/links, since MKDEV() expect that the max bits of
+	 * first_minor is 20.
 	 */
 	disk->first_minor = index << part_shift;
-	if (disk->first_minor > 0xff) {
+	if (disk->first_minor > MINORMASK) {
 		err = -EINVAL;
 		goto out_free_idr;
 	}