1.1 --- a/lemon/concepts/maps.h	Wed Sep 30 08:36:43 2009 +0200
     1.2 +++ b/lemon/concepts/maps.h	Wed Sep 30 08:41:06 2009 +0200
     1.3 @@ -182,7 +182,8 @@
     1.4  
     1.5        template<typename _ReferenceMap>
     1.6        struct Constraints {
     1.7 -        void constraints() {
     1.8 +        typename enable_if<typename _ReferenceMap::ReferenceMapTag, void>::type
     1.9 +        constraints() {
    1.10            checkConcept<ReadWriteMap<K, T>, _ReferenceMap >();
    1.11            ref = m[key];
    1.12            m[key] = val;