# Numbering of appendices in the backmatter of a book

I'm using the standard book class. If I write

\documentclass{book}

\begin{document}

\frontmatter
\tableofcontents

\mainmatter
\chapter{foo}
\section{Donald}

\backmatter
\chapter{bar}
\section{Mickey}

\end{document}

I expect to have chapter bar numbered as appendix A and section Mickey as A.1. Instead chapter bar is not numbered and section Mickey is 1.2, following section Donald. If I insert the appendix command to obtain

\documentclass{book}

\begin{document}

\frontmatter
\tableofcontents

\mainmatter
\chapter{foo}
\section{Donald}

\backmatter
\appendix
\chapter{bar}
\section{Mickey}

\end{document}

then chapter bar is unnumbered and section Mickey is numbered as .1.

What am I doing wrong?

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