diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_geometry_traits/Circle_segment_2.h b/Arrangement_on_surface_2/include/CGAL/Arr_geometry_traits/Circle_segment_2.h
index 82b40648ecb..fba31c556be 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_geometry_traits/Circle_segment_2.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_geometry_traits/Circle_segment_2.h
@@ -143,7 +143,7 @@ public:
     return !equals(p);
   }
 
-  bool operator == (const Self& p)
+  bool operator == (const Self& p) const
   {
     return equals(p);
   }