From e47669107b493da9fd039fc7c2dd3f4666d03be1 Mon Sep 17 00:00:00 2001
From: Daniel Arndt <daniel.arndt@iwr.uni-heidelberg.de>
Date: Thu, 9 Aug 2018 11:22:08 +0200
Subject: [PATCH] Add check for level difference in
 update_periodic_face_map_recursively

---
 source/grid/tria.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/source/grid/tria.cc b/source/grid/tria.cc
index 5b96819c29..053a255cc0 100644
--- a/source/grid/tria.cc
+++ b/source/grid/tria.cc
@@ -951,6 +951,8 @@ namespace
     Assert(face_1->at_boundary() && face_2->at_boundary(),
            ExcMessage("Periodic faces must be on the boundary"));
 
+    Assert(std::abs(cell_1->level() - cell_2->level()) < 2, ExcInternalError());
+
     // insert periodic face pair for both cells
     using CellFace =
       std::pair<typename Triangulation<dim, spacedim>::cell_iterator,
-- 
2.39.5