diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_polyline_traits_2.h b/Arrangement_on_surface_2/include/CGAL/Arr_polyline_traits_2.h
index 1a9deaa38d7..bcdebacad3b 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_polyline_traits_2.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_polyline_traits_2.h
@@ -1328,6 +1328,7 @@ public:
     Merge_2(const Geometry_traits* traits) : m_poly_traits(traits) {}
 
     /*!
+     * TODO: Consider the orientation of the cv1 and cv2!!!
      * Merge two given x-monotone curves into a single curve(segment).
      * \param cv1 The first curve.
      * \param cv2 The second curve.