diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 218aa7e41970..37994a7a1b6f 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1708,7 +1708,8 @@ static int nbd_dev_add(int index)
 		if (err == -ENOSPC)
 			err = -EEXIST;
 	} else {
-		err = idr_alloc(&nbd_index_idr, nbd, 0, 0, GFP_KERNEL);
+		err = idr_alloc(&nbd_index_idr, nbd, 0,
+				(MINORMASK >> part_shift) + 1, GFP_KERNEL);
 		if (err >= 0)
 			index = err;
 	}