jasmine.js expect() does not work inside an asynchronous callback

I'm getting acquainted with Jasmine (http://pivotal.github.com/jasmine/) and found something rather baffling:

it("should be able to send a Ghost Request", function() {
  var api = fm.api_wrapper;

  api.sendGhostRequest(function(response) {
    console.dir('server says: ', response);
  });

  expect(true).toEqual(false);
});

Fails as expected.

However, moving the expect call inside the callback:

it("should be able to send a Ghost Request", function() {
  var api = fm.api_wrapper;

  api.sendGhostRequest(function(response) {
    console.dir('server says: ', response);
    expect(true).toEqual(false);
  });
});

Somehow passes :O

After some debugging: api.sendGhostRequest() does an asynchronous ajax request, and jasmine rushes past before the request has completed.

Hence the question:

How do I get jasmine to wait for ajax execution before ascertaining the test result?