diff --git a/Manage.c b/Manage.c
index 225af81..2e602d7 100644
--- a/Manage.c
+++ b/Manage.c
@@ -781,7 +781,8 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 		}
 
 		/* Make sure device is large enough */
-		if (tst->ss->avail_size(tst, ldsize/512, INVALID_SECTORS) <
+		if (tst->sb &&
+		    tst->ss->avail_size(tst, ldsize/512, INVALID_SECTORS) <
 		    array_size) {
 			if (dv->disposition == 'M')
 				return 0;