diff --git a/Packages/Planar_map/include/CGAL/IO/write_pm.h b/Packages/Planar_map/include/CGAL/IO/write_pm.h
index 765d584b502..1e8de63b881 100644
--- a/Packages/Planar_map/include/CGAL/IO/write_pm.h
+++ b/Packages/Planar_map/include/CGAL/IO/write_pm.h
@@ -48,7 +48,7 @@ CGAL_BEGIN_NAMESPACE
 template <class PM, class Writer>
 void write_pm( const PM& pm,
                Writer& writer, 
-               std::ostream& o) 
+               std::ostream&) 
 {
 
   //typedef Planar_map_2<Dcel,Traits>                     PM;