diff --git a/Packages/Triangulation_2/changes.txt b/Packages/Triangulation_2/changes.txt
index c39b3243023..f14fd199c77 100644
--- a/Packages/Triangulation_2/changes.txt
+++ b/Packages/Triangulation_2/changes.txt
@@ -1,6 +1,10 @@
 Package triangulation: provides triangulations Delaunay triangulations, 
 constrained and regular triangulations with  tests and examples.
 
+Ver 7.53
+- fixed a long line in Trivial_iterator.h
+- fixed is_valid() and mirror_vertex in  Triangulation_ds_face_2.h
+
 Ver 7.52 (12/11/02)
 - fixes is_valid() de Triangulation_ds_face_2.h
   to deal with data structure when two faces can share 3 vertices 
diff --git a/Packages/Triangulation_2/examples/Triangulation_2/terrain.C b/Packages/Triangulation_2/examples/Triangulation_2/terrain.C
index d460c813533..f403bda80ef 100644
--- a/Packages/Triangulation_2/examples/Triangulation_2/terrain.C
+++ b/Packages/Triangulation_2/examples/Triangulation_2/terrain.C
@@ -20,6 +20,7 @@ int main()
 
   Delaunay dt;
   dt.insert(begin, end);
+  std::cout << dt.number_of_vertices() << std::endl;
   return 0;
 }
 
diff --git a/Packages/Triangulation_2/include/CGAL/Triangulation_ds_face_2.h b/Packages/Triangulation_2/include/CGAL/Triangulation_ds_face_2.h
index 849565e5bb0..f9899d3c936 100644
--- a/Packages/Triangulation_2/include/CGAL/Triangulation_ds_face_2.h
+++ b/Packages/Triangulation_2/include/CGAL/Triangulation_ds_face_2.h
@@ -127,7 +127,7 @@ typename Triangulation_ds_face_2<Tds>::Vertex_handle
 Triangulation_ds_face_2<Tds>::
 mirror_vertex(int i) const
 {
-  CGAL_triangulation_precondition ( neighbor(i) != NULL);
+  CGAL_triangulation_precondition ( neighbor(i) != NULL &&  dimension() >= 1);
   //return neighbor(i)->vertex(neighbor(i)->index(this->handle()));
   return neighbor(i)->vertex(mirror_index(i));
 }
@@ -138,8 +138,8 @@ Triangulation_ds_face_2<Tds>::
 mirror_index(int i) const
 {
   // return the index of opposite vertex in neighbor(i);
-  CGAL_triangulation_precondition (neighbor(i) != NULL);
-  //return neighbor(i)->index(this->handle());
+  CGAL_triangulation_precondition (neighbor(i) != NULL &&  dimension() >= 1);
+  if (dimension() == 1) return neighbor(i)->index(this->handle());
   return ccw( neighbor(i)->index(vertex(ccw(i))));
 }
 
@@ -210,10 +210,12 @@ is_valid(bool verbose, int level) const
   bool result = Fb::is_valid(verbose, level);
   for(int i = 0; i <= dimension(); i++) {
     Face_handle n = neighbor(i);
-    // MK: this needs to be changed so that we get the correct index
-    // when we have two faces with two common edges
-    //    int in = n->index(this->handle());
-    int in = n->index(mirror_vertex(i));
+    // the strange formulation in case dimension()==2 
+    // is used to handle the cases of TDS allowing
+    // two faces with two common edges
+    int in;
+    if (dimension() == 0) in = n->index(this->handle());
+    else in = n->index(mirror_vertex(i));
     result = result && ( this->handle() == n->neighbor(in) );
     switch(dimension()) {
     case 0 :