Why do I get an error trying to call a template member function with an explicit type parameter?

I don't get it, it seems to me that the call to f is completely unambiguous, but it fails to compile with expected primary-expression before ‘int’. If I comment out the line with the call to f, it compiles fine.

template<typename T>
struct A {
    template<typename S>
    void f() { }
};

template<typename T>
struct B : A<T> {
    void g() {
        this->f<int>();
    }
};