Syntax Error in 2.0.2: Readline Library

I'm using the Ruby 'Readline' library, which is described in the PickAxe book as an 'interface to GNU Readline library'

The relevant code looks like:
  require 'readline'
  include Readline
  cmd = readline("prompt > ", true)

RubyMine has problems with this code:
- says it can't locate "include 'readline'"
- can't jump to the Readline method definition using Ctrl-B
- shows a red syntax error under 'cmd=readline...'

I'm using:
RubyMine 2.0.2
Ruby 1.8.7
Ubuntu Jaunty