Hello *! I defined a custom bidi-iterator and assumed it was going to support std::advance(iterator, Difference n), where n can be negative for random access and bidirectional iterators. The definition of my iterator's facade base looks like: struct my_iter : boost::iterator_facade < my_iter , const byte , boost::bidirectional_traversal_tag , const byte > { // some impl stuff follows... }; My tests show that calling: advance(instance_of_my_iter, N) works fine (increment implementation is called) advance(instance_of_my_iter, -N) does not work, because increment (instead of decrement) is called as well While reading through the docs for iterator facade at http://www.boost.org/doc/libs/1_46_0/libs/iterator/doc/iterator_facade.html I found the section iterator_facade Core Operations. For the advance implementation is stated there that it is only gets called for Random Access Iterators. C++ Standard clearly defines that N-Parameter to std::advance can be negative to random access and bidi iterators. Implementing void advance member in my_iter still results in the call to increment member. Can someone give me any suggestions or is it a bug in the iterator lib? My compiler is gcc 4.3 under Debian Linux with Kernal 2.6.26. and Boost 1.42. With Kind Regards, Ovanes