You could change zip_iterator.hpp:319 to //bool tuple_equal(tuples::null_type, tuples::null_type) //{ return true; } template<typename Tuple1, typename Tuple2> bool tuple_equal( Tuple1 const& t1, Tuple2 const& t2 ) { return t1==t2; } This assumes that the comparison operator for tuples works on your compiler as described by the comment in zip_iterator.hpp. This is what I did. Otherwise you could change it to (untested): template<typename Tuple1, typename Tuple2> bool tuple_equal( Tuple1 const& t1, Tuple2 const& t2 ) { return t1.get_head() == t2.get_head() && tuple_equal(t1.get_tail(), t2.get_tail()); } template<> bool tuple_equal<tuples::null_type, tuples::null_type>( const tuples::null_type&, const tuples::null_type&) { return true; } _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/