pip requres doesn't install eventlet properly

When trying to installl eventlet using the virtualenv install script, the following error occurs:
  Downloading eventlet-0.9.10.tar.gz (300Kb): 300Kb downloaded
  Running setup.py egg_info for package eventlet
    Traceback (most recent call last):
      File "eventlet/__init__.py", line 5, in <module>
        from eventlet import greenthread
      File "eventlet/greenthread.py", line 3, in <module>
        from eventlet import event
      File "eventlet/event.py", line 1, in <module>
        from eventlet import hubs
      File "eventlet/hubs/__init__.py", line 3, in <module>
        from eventlet.support import greenlets as greenlet
      File "eventlet/support/greenlets.py", line 2, in <module>
        import greenlet
    ImportError: No module named greenlet
I assume there is a missing require on a package called greenlet?