diff --git a/include/boost/iterator/iterator_concepts.hpp b/include/boost/iterator/iterator_concepts.hpp
index 50e5546..26a23c9 100644
--- a/include/boost/iterator/iterator_concepts.hpp
+++ b/include/boost/iterator/iterator_concepts.hpp
@@ -105,6 +105,7 @@ namespace boost_concepts {
       void constraints()
       {
         const value_type& r = *i;
+        boost::ignore_unused_variable_warning(r);
       }
     Iterator i;
   };