ломается цепочка вызовов параметризованных методов

struct Accessor{
    template <typename A> void plot(A &a) const { 
        a.plot_impl<0>(*this); 
    }
};

struct XXX{
    template <int I> void plot_impl(const Accessor&){}
    void plot(const Accessor &acc){ acc.plot(*this); }
};

$ g++ -std=c++11 -c test-accessor.cpp
test-accessor.cpp: In instantiation of ‘void Accessor::plot(A&) const [with A = XXX]’:
test-accessor.cpp:9:48:   required from here
test-accessor.cpp:3:14: error: invalid operands of types ‘<unresolved overloaded function type>’ and ‘int’ to binary ‘operator<’
   a.plot_impl<0>(*this);
   ~~~~~~~~~~~^~