diff --git a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Corefinement/intersection_impl.h b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Corefinement/intersection_impl.h
index 430b96b87b2..f5d7471ecd6 100644
--- a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Corefinement/intersection_impl.h
+++ b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/Corefinement/intersection_impl.h
@@ -353,6 +353,8 @@ class Intersection_of_triangle_meshes
     }
 
     Key key(ipt.type_1, ipt.type_2, h1, h2);
+    if (&tm1==&tm2 && h1>h2)
+      key=Key(ipt.type_2, ipt.type_1, h2, h1);
 
     std::pair<typename std::map<Key,Node_id>::iterator,bool> res=
       coplanar_node_map.insert(std::make_pair(key,current_node+1));