# Possible bug of mhchem package v4.05

It is an error arise with package option \mhchemoptions{arrows=pgf} after last update 2016-08-08 to v4.05. Somebody can confirm?

\documentclass[]{article}
\RequirePackage[version=4]{mhchem}
\mhchemoptions{arrows=pgf}

\begin{document}
\ce{2H2 + O2 -> 2H2O}
\end{document}

• Works if you do \usepackage[version=4,arrows=pgf]{mhchem}. I think this might be the intended behaviour, if I understand the manual correctly. – Torbjørn T. Oct 8 '16 at 16:34

If you write \usepackage[version=4,arrows=pgf]{mhchem}, mhchem loads the respective TikZ package automatically. (The same thing should happen with \RequirePackage.) When you switch to pgf arrows in another matter, after initial loading of the package, you have to make sure the TikZ package is already requested by some other means (e.g. you writing \usepackage{tikz}).