diff --git a/TDS_3/include/CGAL/Triangulation_simplex_3.h b/TDS_3/include/CGAL/Triangulation_simplex_3.h
index 8bb4188f442..0754fb021c5 100644
--- a/TDS_3/include/CGAL/Triangulation_simplex_3.h
+++ b/TDS_3/include/CGAL/Triangulation_simplex_3.h
@@ -96,8 +96,10 @@ public:
 
   // returns the dimension of the simplex
   int dimension () const {
-    return (ref & 3);
+    if(ref == -1) return -1;
+    else return (ref & 3);
   }
+
   // returns an incident cell:
   Cell_handle incident_cell() {
     return ch;
@@ -161,6 +163,7 @@ operator==(Triangulation_simplex_3<TriangulationDataStructure_3> s0,
   typename Sim::Cell_handle neighbor;
 
   switch (s0.dimension()) {
+  case -1: return s1.dimension() == -1;
   case (0): // Vertex
     return (s0.ch->vertex(s0.index(0)) == s1.ch->vertex(s1.index(0)));
   case (1): // Edge