form_for doesn't work with an uncountable route

def new
  @news = News.new 
end

<% form_for(@news) do |f| %>
...
<% end %>

This code throws error:

ActionView::TemplateError (news_url failed to generate from {:action=>"show", :controller=>"news"} - you may have ambiguous routes, or you may need to supply additional parameters for this route. content_url has the following required parameters: ["news", :id] - are they all satisfied?)

As workaround i use more verbose version of form_for:

<% form_for(:news, news_index_url) do |f| %>
...
<% end %>

But it would be better to use same syntax in case of uncountable resources.