scope form_for error

I have a route that looks like this:

scope ':project_name' do   resources :submissions end

and a form_for tag that looks like this:

= form_for admin_submission_path(@project.name, @submission), :html => { :multipart => true } do |f|

but for some reason it tries to match the show route instead and returns a no route error. There seems to be some solutions on stackoverflow but they look pretty messy to me:

http://stackoverflow.com/questions/3741979/form-for-and-scopes-rails-3

BTW, there is an admin namespace in the route:

namespace :admin do   scope ':project_name' do     resources :submissions   end end