[AUCTeX] Citation completion

[Chris Mears]

Hi,

I have a problem with citation completion.  I have a bibliography file,
'books.bib':

    @Article{guy00:_fancy_title,
      author =       {Some Guy},
      title =        {Fancy Title},
      journal =      {Journal of High Regard},
      year =         2000}

and a document 'article.tex':

    \documentclass{article}

    \begin{document}

    Lorem ipsum dolor sit amet...

    \bibliographystyle{plain}
    \bibliography{books}

    \end{document}

Parsing the tex file (with C-c C-n) gives the variable
LaTeX-bibliography-list the value

    (("books") nil)

which seems correct.  However, the variable LaTeX-bibitem-list is nil,
which means that I get no completion for \cite (and \citep etc.)
commands.

What have I done wrong?

Thanks,
Chris Mears