diff --git a/midx.c b/midx.c
index 07b3981a7a..64a051cca1 100644
--- a/midx.c
+++ b/midx.c
@@ -338,9 +338,11 @@ struct object_id *nth_midxed_object_oid(struct object_id *oid,
 					struct multi_pack_index *m,
 					uint32_t n)
 {
-	if (n >= m->num_objects)
+	if (n >= m->num_objects + m->num_objects_in_base)
 		return NULL;
 
+	n = midx_for_object(&m, n);
+
 	oidread(oid, m->chunk_oid_lookup + st_mult(m->hash_len, n),
 		the_repository->hash_algo);
 	return oid;