diff --git a/Nef_3/include/CGAL/Nef_polyhedron_3.h b/Nef_3/include/CGAL/Nef_polyhedron_3.h
index 6f69d69fad9..1bbf2518398 100644
--- a/Nef_3/include/CGAL/Nef_polyhedron_3.h
+++ b/Nef_3/include/CGAL/Nef_polyhedron_3.h
@@ -164,7 +164,7 @@ class Nef_polyhedron_3 : public CGAL::Handle_for< Nef_polyhedron_3_rep<Kernel_,
   typedef typename Kernel::Segment_3                  Segment_3;
   typedef typename Kernel::Aff_transformation_3       Aff_transformation_3;
 
-if _MSC_VER >= 1900
+#if _MSC_VER >= 1900
   // VC++ < 2017 has a problem to digest the following typedef,
   // and does not need the using statements -- AF
   // The left and right part of these typedefs have the same name. It is