# eqref in captions with mathtools

I've now tried mathtools for the first time, for the sake of showonlyrefs. It works fine, except if I put an \eqref command into a figure caption, in which case I get:

! Argument of \@caption has an extra }.
! Paragraph ended before \@caption was complete.


Here is the MWE:

\documentclass{article}
\usepackage{amsmath}
\usepackage{mathtools}
\mathtoolsset{showonlyrefs=true,showmanualtags=true} % do not number unreferenced equations
\begin{document}
$$\label{eq:EVE-HEH} x$$
\begin{figure}
\caption{See eigenvalue equation \eqref{eq:EVE-HEH}.}
\end{figure}
\end{document}


What do I do wrong?

Update: Found here that \protect before \eqref in caption helps, and indeed it does. However this is not mentioned in the mathtools. Is it the right solution?

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## 1 Answer

Unfortunately \eqref is not a robust command, so it needs \protect in front of it when used in a moving argument, such as the argument of \caption or \section.

If you happen to use many times \eqref in such places, you can consider "robusting" it:

\usepackage{fixltx2e,amsmath}
\MakeRobust{\eqref}


Note that \eqref is provided by amsmath, rather than mathtools (this last package loads amsmath).

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