Implementing ActiveRecord named scopes with a module

Item.rb

class Item < ActiveRecord::Base
  extend SpecialScopes
end

special_scopes.rb

module SpecialScopes
  def self.extended(base)
    base.class_eval do
      scope :paid, where(:paid => true)
    end
  end
end

This code compiles and runs, but Item.paid doesn't exist and can't be used.