diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_rational_arc_traits_2.h b/Arrangement_on_surface_2/include/CGAL/Arr_rational_arc_traits_2.h
index 86dd17f9e78..341d3eb9d36 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_rational_arc_traits_2.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_rational_arc_traits_2.h
@@ -269,7 +269,7 @@ public:
      * \param cv The curve.
      * \return (true) if the curve is a vertical segment; (false) otherwise.
      */
-    bool operator() (const X_monotone_curve_2& cv) const
+    bool operator() (const X_monotone_curve_2&) const
     {
       // A rational function can never be vertical:
       return (false);