How do I port this root path with a subdomain constraint to Rails 4?

We have an app an upgrading from Rails 3.2 to 4.0.

The 3.2 version has roots all over routes.rb, which I ported to the new syntax, but I am not quite sure how to handle the subdomain constraint.

In 3.2:

  constraints(SubDomain) do
    root to: "companies#index"
    ...
  end

I tried to port it like the other root paths, but it looks like there is a conflict on the non-constrained root path.

Here is what I tried:

  constraints(SubDomain) do
    get "/", to: "companies#index", as: :root
    ...
  end

And the error:

/Users/blu/.rvm/gems/ruby-2.1.7/gems/actionpack-4.0.13/lib/action_dispatch/routing/route_set.rb:430:in add_route': Invalid route name, already in use: 'root' (ArgumentError) You may have defined two routes with the same name using the:asoption, or you may be overriding a route already defined by a resource with the same naming. For the latter, you can restrict the routes created withresourcesas explained here: http://ift.tt/1g4FQcF from /Users/blu/.rvm/gems/ruby-2.1.7/gems/actionpack-4.0.13/lib/action_dispatch/routing/mapper.rb:1484:in add_route'

Any help on the correct syntax here would be great, thanks.