diff --git a/STL_Extension/doc/STL_Extension/CGAL/Iterator_range.h b/STL_Extension/doc/STL_Extension/CGAL/Iterator_range.h
index 8d68f9f5b98..88d0c828276 100644
--- a/STL_Extension/doc/STL_Extension/CGAL/Iterator_range.h
+++ b/STL_Extension/doc/STL_Extension/CGAL/Iterator_range.h
@@ -62,10 +62,10 @@ namespace CGAL {
   }
 
   /// returns `std::distance(begin(), end())`
-  typename std::iterator_traits<I>::difference_type
+  std::size_t
   size() const
   {
-    return std::distance(begin(), end());
+    return static_cast<std::size_t>(std::distance(begin(), end()));
   }
 };
 
diff --git a/STL_Extension/include/CGAL/Iterator_range.h b/STL_Extension/include/CGAL/Iterator_range.h
index 338b0b41c68..9267717bfb5 100644
--- a/STL_Extension/include/CGAL/Iterator_range.h
+++ b/STL_Extension/include/CGAL/Iterator_range.h
@@ -65,10 +65,10 @@ namespace CGAL {
   }
 
   /// returns `std::distance(begin(), end())`
-  typename std::iterator_traits<I>::difference_type
+  std::size_t
   size() const
   {
-    return std::distance(begin(), end());
+    return static_cast<std::size_t>(std::distance(begin(), end()));
   }
 
   /// returns `std::distance(begin(), end())==0`