named_scope doesn't work when 2 procs expect arguments

Mixing 2 named_scopes that accepts arguments raises the following error depending on the order that the scopes are executed:

ArgumentError: wrong number of arguments (2 for 0)
 from (__DELEGATION__):2:in `sort_by'
 from (__DELEGATION__):2:in `__send__'
 from (__DELEGATION__):2:in `sort_by'
 from (irb):1

This will work:

User.sort_by(:name, :desc).by_country('us')

But this won't:

User.by_country('us').sort_by(:name, :desc)

Here's what the model looks like:

class User < ActiveRecord::Base
  named_scope :sort_by, Proc.new { |attr, order|
    order ||= 'asc'
    {:order => "#{attr} #{order}"}
  }

  named_scope :by_country, Proc.new { |code|
    {:conditions => {:country_code => code.to_s}}
  }
end