diff --git a/Arrangement_on_surface_2/include/CGAL/Sweep_line_2/Arr_overlay_traits_2.h b/Arrangement_on_surface_2/include/CGAL/Sweep_line_2/Arr_overlay_traits_2.h
index e23b724995a..7ab53d3113d 100644
--- a/Arrangement_on_surface_2/include/CGAL/Sweep_line_2/Arr_overlay_traits_2.h
+++ b/Arrangement_on_surface_2/include/CGAL/Sweep_line_2/Arr_overlay_traits_2.h
@@ -719,7 +719,7 @@ public:
                                       Arrangement_blue_2>;
     
   public:
-    Comparison_result operator() (const X_monotone_curve_2 & xcv) const
+    bool operator() (const X_monotone_curve_2 & xcv) const
     {
       return m_base_is_vert (xcv.base());
     }