Does longtable not support the m column type?

Question

I have the following problem: I would like to use the m column type in a longtable. But if I typeset

\documentclass{minimal}
\usepackage{longtable}
\begin{document}
    \begin{longtable}{p{5cm}m{5cm}}
        skdlbf & asljkdh\\
    \end{longtable}
\end{document}

I get an error about an Illegal character in array arg in the line of \begin{longtable}{..}. If I change the m to a p, all runs well.

So why does longtable not support the m (and b) column type? Am I missing a package?

Answer 1

\usepackage{array}

That's the solution.