diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_topology_traits/Arr_spherical_topology_traits_2_impl.h b/Arrangement_on_surface_2/include/CGAL/Arr_topology_traits/Arr_spherical_topology_traits_2_impl.h
index 93134d03076..13ec1ea8108 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_topology_traits/Arr_spherical_topology_traits_2_impl.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_topology_traits/Arr_spherical_topology_traits_2_impl.h
@@ -567,6 +567,7 @@ Arr_spherical_topology_traits_2<GeomTraits, Dcel>::
 erase_redundant_vertex(Vertex * v)
 {
   CGAL_assertion_msg(0, "Not implemented!");
+  return NULL;
 }
 
 /*! \brief obtains the curve associated with a boundary vertex */