diff --git a/Arrangement_on_surface_2/include/CGAL/Arr_spherical_arc_traits_2.h b/Arrangement_on_surface_2/include/CGAL/Arr_spherical_arc_traits_2.h
index 9fc9fa50cd4..42233700ff0 100644
--- a/Arrangement_on_surface_2/include/CGAL/Arr_spherical_arc_traits_2.h
+++ b/Arrangement_on_surface_2/include/CGAL/Arr_spherical_arc_traits_2.h
@@ -20,7 +20,7 @@
 #ifndef CGAL_ARR_SPHERICAL_ARC_TRAITS_2_H
 #define CGAL_ARR_SPHERICAL_ARC_TRAITS_2_H
 
-//#define CGAL_ARR_PLANE
+#define CGAL_ARR_PLANE
 
 /*! \file
  * The spherical_arc traits-class for the arrangement package.