autonum does not like \ref in a \caption

Question

The following is a minimal non-working example of a reference to some label within a caption while using the autonum package.

\documentclass{article}
\usepackage{autonum}
\begin{document}

\begin{align}
    E = mc^2 \label{eq::label}
\end{align}

\begin{figure}
    y \caption{ \ref{eq::label} }
\end{figure}

\end{document}

Upon compiling I get the following errors:

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

I get the same result, if I refer to, say another figure, instead of an equation.

How can I avoid this error?

Answer 1

Use \protect

\caption{\protect\ref{eq::label}}