ublas::vector in std::map

Hi,

I tried using a ublas vector as key type in a std::map along the lines of

boost::ublas::vector<double> x(2);
std::map<boost::ublas::vector<double>, int> vm;
vm[x] = 1;

which wont compile (gcc 4.0.3) due to

/usr/lib/gcc/x86_64-linux-gnu/4.0.3/../../../../include/c++/4.0.3/bits/stl_function.h:227: error: no match
for ‘operator<’ in ‘__x < __y’.

Adding an implementation of

bool operator<(boost::ublas::vector<double> const& A, boost::ublas::vector<double> const& B) {...}

unfortunately doesnt help. Could anyone please point out what I am missing?