diff --git a/Straight_skeleton_2/examples/Straight_skeleton_2/Show_straight_skeleton.cpp b/Straight_skeleton_2/examples/Straight_skeleton_2/Show_straight_skeleton.cpp
index 143fc4bdae1..8a4aed5e198 100644
--- a/Straight_skeleton_2/examples/Straight_skeleton_2/Show_straight_skeleton.cpp
+++ b/Straight_skeleton_2/examples/Straight_skeleton_2/Show_straight_skeleton.cpp
@@ -37,6 +37,27 @@ int main( int argc, char* argv[] )
     {
       is >> input ;
       
+      //check the validity of the input and fix orientation
+      if (!input.outer_boundary().is_simple())
+      {
+        std::cerr << "ERROR: outer boundary is not simple.";
+        return 1;
+      }
+      if ( input.outer_boundary().is_clockwise_oriented() )
+        input.outer_boundary().reverse_orientation();
+      int k=0;
+      for (Polygon_with_holes::Hole_iterator it = input.holes_begin();
+                                             it!=input.holes_end(); ++it, ++k)
+      {
+        if (!it->is_simple())
+        {
+          std::cerr << "ERROR: hole "<< k << " is not simple.\n";
+          return 1;
+        }
+        if (it->is_counterclockwise_oriented())
+          it->reverse_orientation();
+      }
+
       Straight_skeleton_ptr ss = CGAL::create_interior_straight_skeleton_2(input);
       if ( ss )
       {