diff --git a/src/core/ndisc/nm-ndisc.c b/src/core/ndisc/nm-ndisc.c
index ed34f088a0..cc2723c44b 100644
--- a/src/core/ndisc/nm-ndisc.c
+++ b/src/core/ndisc/nm-ndisc.c
@@ -768,7 +768,7 @@ nm_ndisc_add_route(NMNDisc *ndisc, const NMNDiscRoute *new_item, gint64 now_msec
         return FALSE;
     }
 
-    g_array_insert_val(rdata->routes, insert_idx == G_MAXUINT ? 0u : insert_idx, *new_item);
+    g_array_insert_val(rdata->routes, insert_idx == G_MAXUINT ? rdata->routes->len : insert_idx, *new_item);
     return TRUE;
 }