diff --git a/GraphicsView/include/CGAL/Qt/Converter.h b/GraphicsView/include/CGAL/Qt/Converter.h
index f8072d37102..ce3f395b35c 100644
--- a/GraphicsView/include/CGAL/Qt/Converter.h
+++ b/GraphicsView/include/CGAL/Qt/Converter.h
@@ -146,7 +146,7 @@ public:
     return QLineF();
   }
 
-  QPolygonF operator()(const CGAL_Triangle_2 &t)
+  QPolygonF operator()(const CGAL_Triangle_2 &t) const
   {
     QPolygonF qp;
     qp << operator()(t.vertex(0)) << operator()(t.vertex(1)) << operator()(t.vertex(2));