# Using sidenotes in mdframed environment

I get problems when I try to use sidenotes in an mdframed environment:

\documentclass{tufte-book}
\usepackage{xcolor}
\usepackage{mdframed}
\newtheorem{mdtheorem}{Theorem}
\newenvironment{theorem}%
{\begin{mdframed}[backgroundcolor=lightgray]\begin{mdtheorem}}%
{\end{mdtheorem}\end{mdframed}}

\begin{document}

\begin{theorem}
test \sidenote{side note}
\end{theorem}

\end{document}


Any ideas how to get around this issue?

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The command \sidenote is equal to \marginpar or \marginnote which are not allowed in tables or boxes. So you can't use them.
The UK FAQ describes this error: ! LaTeX Error: Float(s) lost.