Using factory_girl_rails with Rspec on namespaced models

I have a web service that serves Ads to several different clients. The structure of the Ad varies between clients, and therefore, I am using namespaces for my models and controllers by the client name to differentiate between Ads. From the high level, it looks like this:

'app/models/client1/ad.rb'

class Client1::Ad < ActiveRecord::Base
  attr_accessible :title, :description
end

'app/models/client2/ad.rb'

class Client2::Ad < ActiveRecord::Base
  attr_accessible :title, :description, :source
end

In reality, these models are more complex and have associations, but that is not the point.
I am writing some unit tests using rspec-rails 2.4.0 and factory_girl_rails 1.0.1, and all of my factories work great. However, I am not able to define factories for the namespaced models. I've tried something like:

Factory.define :client1_ad, :class => Client1::Ad do |ad|
  ad.title       "software tester"  
  ad.description "Immediate opening"
end  

and

Factory.define :client2_ad, :class => Client2::Ad do |ad|
  ad.title       "software tester"  
  ad.description "Immediate opening"
  ad.source      "feed"
end

It didn't do the job. I looked around, but every single example that I saw was using non-namespaced models. Anyone have any ideas? Any input is greatly appreciated.