diff --git a/Packages/Alpha_shapes_3/include/CGAL/Alpha_shape_3.h b/Packages/Alpha_shapes_3/include/CGAL/Alpha_shape_3.h
index 2c4b9b539a1..87dacd9f166 100644
--- a/Packages/Alpha_shapes_3/include/CGAL/Alpha_shape_3.h
+++ b/Packages/Alpha_shapes_3/include/CGAL/Alpha_shape_3.h
@@ -1796,8 +1796,8 @@ Alpha_shape_3<Dt>::find_optimal_alpha(const int& nb_components)
   Alpha_iterator last = alpha_end();
   Alpha_iterator middle;
   
-  ptrdiff_t len = last - first - 1;
-  ptrdiff_t half;
+  std::ptrdiff_t len = last - first - 1;
+  std::ptrdiff_t half;
 
   while (len > 0)
     {