diff --git a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_slicer.h b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_slicer.h
index 3d30cc4b8af..4a6ce096713 100644
--- a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_slicer.h
+++ b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_slicer.h
@@ -179,7 +179,7 @@ class Polygon_mesh_slicer
         );
         typename cpp11::result_of<typename Traits_::Intersect_3(Plane_3, Segment_3)>::type
           inter = intersect_3(m_plane, s);
-        CGAL_assertion( inter );
+        CGAL_assertion(inter != boost::none);
         const Point_3* pt_ptr = boost::get<Point_3>(&(*inter));
         current_poly.push_back( *pt_ptr );
       }