error output

$ ruby ice_nine_delegator.rb                                                                                                                                                                                                                                         [11:18:34]
/Users/cyrilmougel/.rbenv/versions/1.9.3-p327-perf/lib/ruby/gems/1.9.1/gems/ice_nine-0.5.0/lib/ice_nine.rb:42:in `block in deep_freeze': undefined method `deep_freeze' for #<Array:0x007f9dd907a660> (NoMethodError)
        from /Users/cyrilmougel/.rbenv/versions/1.9.3-p327-perf/lib/ruby/gems/1.9.1/gems/ice_nine-0.5.0/lib/ice_nine/support/recursion_guard.rb:25:in `guard'
        from /Users/cyrilmougel/.rbenv/versions/1.9.3-p327-perf/lib/ruby/gems/1.9.1/gems/ice_nine-0.5.0/lib/ice_nine.rb:41:in `deep_freeze'
        from ice_nine_delegator.rb:10:in `<main>'

ice_nine_delegator.rb

require 'delegate'
require 'ice_nine'

class Foo < SimpleDelegator
  def initialize(hash)
    __setobj__(hash)
  end
end

IceNine.deep_freeze(Foo.new({:bar => 'baz'}))