You shouldn't be reopening this module.  The modules rspec-core uses to organize it's internal code are not part of the public interface of rspec-core and are subject to changing w/o notice.  Instead, I would do this:

``` ruby
require 'rspec/core' # so RSpec.configure is available

module RSpec
  module Its
    def its(attribute, &block)
    end
  end
end

RSpec.configure do |rspec|
  rspec.extend RSpec::Its
end
```

Basically, put the code in your own module, and use `RSpec::Configuration#extend` to ensure your module is extended onto all example groups.  That is part of RSpec's public API.