the logical not operator not working in boost::spirit::qi

the logical not operator not working in boost::spirit::qi

if in a qi::grammar I use this base rule
expression = (boost::spirit::ascii::string("aaa"));
it will parse "aaa" and nothing else
when I use this one ( notice the ! ) it parses nothing at all while I
expect it to be successful on everything but "aaa"
expression = !(boost::spirit::ascii::string("aaa"));
Could I be missing some include? I'm using boost 1.54.0.