diff --git a/Number_types/include/CGAL/leda_integer.h b/Number_types/include/CGAL/leda_integer.h
index 6f67aaa9806..48f1a513e4f 100644
--- a/Number_types/include/CGAL/leda_integer.h
+++ b/Number_types/include/CGAL/leda_integer.h
@@ -84,8 +84,9 @@ template <> class Algebraic_structure_traits< leda_integer >
         typedef Type& third_argument_type; 
         typedef Type& fourth_argument_type; 
         typedef void result_type;
+        typedef Arity_tag< 4 >         Arity;
         
-        void operator()(const Type& x, const Type& y, Type& q, Type& r){
+        void operator()(const Type& x, const Type& y, Type& q, Type& r) const {
             
             q = x / y;             
             r = x - q*y;