diff --git a/Arrangement_on_surface_2/doc/Arrangement_on_surface_2/CGAL/Arr_observer.h b/Arrangement_on_surface_2/doc/Arrangement_on_surface_2/CGAL/Arr_observer.h
index 99abf22396f..3b7001a984a 100644
--- a/Arrangement_on_surface_2/doc/Arrangement_on_surface_2/CGAL/Arr_observer.h
+++ b/Arrangement_on_surface_2/doc/Arrangement_on_surface_2/CGAL/Arr_observer.h
@@ -3,9 +3,8 @@ namespace CGAL {
 /*! \ingroup PkgArrangementOnSurface2Ref
  *
  * `Arr_observer<Arrangement_2>` is an alias for
- * Aos_observer<Arrangement_on_surface_2>`,
- * where `Arrangement_2` derives from `Arrangement_on_surface_2` and the latter
- * is an instance of the template
+ * `Aos_observer<Arrangement_on_surface_2>`, where `Arrangement_2` derives from
+ * `Arrangement_on_surface_2` and the latter is an instance of the template
  * `CGAL::Arrangement_on_surface_2<GeometryTraits, TopologyTraits>`.
  */