Getting Puma to listen for all hosts with the Guardfile

This has been bugging me for a while, and I've finally had time to track down how to configure Guardfile in order to have Puma listen to all ip addresses.

guard 'rails', :host => '0.0.0.0' do
  watch('Gemfile.lock')
  watch(%r{^(config|lib)/.*})
end

Adding the :host => '0.0.0.0' gets puma to listen for all addresses.