Can't recognise ember nested route

I have the following router:

  this.route('app', function () {
    this.resource('profile', {path: 'profile/profile_id'});
    this.route('connections', function () {
    });

However when I access http://localhost:4200/app/profile/

or

http://localhost:4200/app/profile/2

I get the errorUncaught UnrecognizedURLError: /app/profile/EmberObject.default.extend.startRouting @

Any ideas what is wrong with my route.