[Rubygems-developers] Can't require 'rubygems/specification' anymore?

[Trans]

  require 'rubygems/specification'
  NameError: uninitialized constant Gem
      from /usr/local/lib/site_ruby/1.8/rubygems/version.rb:28
      from /usr/local/lib/site_ruby/1.8/rubygems/specification.rb:7:in
`require'
      from /usr/local/lib/site_ruby/1.8/rubygems/specification.rb:7
      from (irb):1:in `require'
      from (irb):1