diff --git a/HalfedgeDS/include/CGAL/HalfedgeDS_iterator_adaptor.h b/HalfedgeDS/include/CGAL/HalfedgeDS_iterator_adaptor.h
index 72ec52c8f58..484b0c1a3e1 100644
--- a/HalfedgeDS/include/CGAL/HalfedgeDS_iterator_adaptor.h
+++ b/HalfedgeDS/include/CGAL/HalfedgeDS_iterator_adaptor.h
@@ -74,7 +74,7 @@ private:
     // in a small inline function, optimizers might like that
     // better than a static function.
     const I& null_iterator() const {
-        static I it = I(); // zero-initialized and a default constructor
+        static const I it = I(); // zero-initialized and a default constructor
         return it;
     }
 public: