linebreak in list in indented theorem

linebreak in list in indented theorem

I'm trying to make an indented theorem environment as in A theoremstyle with complete indentation using amsthm.
Here's a minimal (non-)working example:
\documentclass{article}
\usepackage{amsthm}
\usepackage[english]{babel}
\usepackage{blindtext}

\makeatletter
  \newtheoremstyle{indent}
  {3pt}% space before
  {3pt}% space after
  {
    \setlength{\leftskip}{2.5em}
    \setlength{\rightskip}{2.5em}
    \addtolength{\@totalleftmargin}{2.5em}
  }% body font
  {}% indent
  {\bfseries}% header font
  {.}% punctuation
  {.5em}% after theorem header
  {}% header specification (empty for default)
\makeatother
\theoremstyle{indent}\newtheorem{theorem}{Theorem}

\begin{document}

\blindtext

\begin{theorem}[correct spacing]
\blindtext
\begin{itemize}
\item This is ok.
\item \blindtext
\end{itemize}
\end{theorem}

\end{document}
Whether or not I add that extra rightskip, my problem is that as soon as an item in a list within my theorem gets longer than one line (as in the third blindtext) it extends over the original right margin of the page, a case not considered in the original post.
Any suggestions?