"invalid deficient type" blunder biased template specialization

the following code:

template <typename s, typename t>
struct foo {
   vacant bar();
};

template <typename t>
void foo <int, t>::bar() {
}

gives me error

invalid deficient form 'struct foo<int, t>'
declaration 'struct foo<int, t>'

(i'm controlling gcc.) syntax biased specialization wrong? note i mislay second argument:

template <typename s>
struct foo {
   vacant bar();
};

template <>
void foo <int>::bar() {
}

then compiles correctly.