diff --git a/Constrained_triangulation_3/include/CGAL/Conforming_constrained_Delaunay_triangulation_vertex_data_3.h b/Constrained_triangulation_3/include/CGAL/Conforming_constrained_Delaunay_triangulation_vertex_data_3.h
index 39b37819855..cd39361f0dd 100644
--- a/Constrained_triangulation_3/include/CGAL/Conforming_constrained_Delaunay_triangulation_vertex_data_3.h
+++ b/Constrained_triangulation_3/include/CGAL/Conforming_constrained_Delaunay_triangulation_vertex_data_3.h
@@ -145,7 +145,7 @@ public:
 
 } // namespace CGAL
 
-#if CGAL_CXX20
+#if CGAL_CXX20 && __cpp_concepts >= 201911L
 #  include <concepts>
 
   static_assert(std::regular<CGAL::Conforming_constrained_Delaunay_triangulation_vertex_data_3>);