Nested routes loads the parent model

Nested routes loads the parent model

I have a nested route structure like this:
App.Router.map(function() {
this.resource('user', {path: '/user/:user_id'}, function() {
this.route('followers', {path: '/followers'});
});
});
when I hit the user/123/followers route I would expect that it
automatically fetch the model from user/123/followers, but it just fetches
the user model from user/123 again. What do I need to add so it fetches
the right data for the route?