diff --git a/Polygon/include/CGAL/Polygon_2.h b/Polygon/include/CGAL/Polygon_2.h
index 919b556d26d..124c7d41f37 100644
--- a/Polygon/include/CGAL/Polygon_2.h
+++ b/Polygon/include/CGAL/Polygon_2.h
@@ -332,7 +332,7 @@ class Polygon_2 {
     //             Miscellaneous
     //--------------------------------------------------------
 
-    int size() const
+  std::size_t size() const
       { return d_container.size(); }
 
     bool is_empty() const