diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 5ac6434..7f1682d 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2634,7 +2634,8 @@ static void check_new_map(struct ceph_mds_client *mdsc,
 		     ceph_mdsmap_is_laggy(newmap, i) ? " (laggy)" : "",
 		     session_state_name(s->s_state));

-		if (memcmp(ceph_mdsmap_get_addr(oldmap, i),
+		if (i >= newmap->m_max_mds ||
+		    memcmp(ceph_mdsmap_get_addr(oldmap, i),
 			   ceph_mdsmap_get_addr(newmap, i),
 			   sizeof(struct ceph_entity_addr))) {
 			if (s->s_state == CEPH_MDS_SESSION_OPENING) {