Rails REST routing: dots in the resource item ID

I have following in my routes.rb:

resources :users, :except => [:new, :create] do
    get 'friends', :as => :friends, :on => :member, :to => "users#friends"
end

and following in my user.rb:

def to_param
  self.login
end

And when, for example, user with dots in login (for example 'any.thing') comes from facebook, rails gives routing error (no route found, I suppose that's because it recognises anything after dot as a format or because of route constraints). How can I come over this error?