BasicObject causing problems with duration.to_json

Heya,
Commit https://github.com/rails/rails/commit/44db47c63e669bdad74e4ac92a79f... caused some problems for us with converting durations to json. Specifically, running -

{:duration => 3.seconds}.to_json

used to return "{'duration':3}" and now returns "{'duration':{}}" on ruby 1.8.7.

I'm currently working around it using :

ActiveSupport::Duration.class_eval do
  def as_json(options = nil)
    to_i
  end
end

Any better suggestions?