Rails 3.1 Capybara jQuery is not defined

I keep on getting this error:

 Failure/Error: page.evaluate_script('jQuery.active') == 0
 Selenium::WebDriver::Error::JavascriptError:
   ReferenceError: jQuery is not defined

whenever I use the script:

wait_until do
  page.evaluate_script('jQuery.active') == 0
end

I've put in a debugger and checked for the jQuery library. It was existing on the particular page.

Is there something I need to configure for this to work?

EDIT:

Versions of Capybara and RSpec are:

rspec-rails-2.11.0 rspec-2.11.0 capybara-1.1.2