mparhack and prelim2e twocolumn bug

[Damien]

There is a bug when using two column mode with mparhack and prelim2e
loaded.

Here is a minimal example:

\documentclass{article}
\usepackage[draft]{prelim2e}
\usepackage{mparhack}
\begin{document}
\twocolumn
foo
\onecolumn
\end{document}

Compiling with pdflatex i get:
Missing number, treated as zero
<to be read again> {
l.10 \onecolumn

Permuting mparhack and prelim2e dosn't change anything.
Does anyone knows a fix?

Thanks!