diff --git a/STL_Extension/include/CGAL/STL_Extension/internal/mesh_option_classes.h b/STL_Extension/include/CGAL/STL_Extension/internal/mesh_option_classes.h
index 587143de0f8..5f94b308737 100644
--- a/STL_Extension/include/CGAL/STL_Extension/internal/mesh_option_classes.h
+++ b/STL_Extension/include/CGAL/STL_Extension/internal/mesh_option_classes.h
@@ -60,7 +60,7 @@ struct Global_optimization_options_base
 
   bool is_max_iteration_number_set() const { return max_it_nb_ != undef_parameter; }
   void set_max_iteration_number(std::size_t i) { max_it_nb_ = i; }
-  int max_iteration_number() const { return max_it_nb_; }
+  std::size_t max_iteration_number() const { return max_it_nb_; }
 
 private:
   double convergence_;