\documentclass{article}
\usepackage{polyglossia} % Remove this line and everything works.
\usepackage{makeidx}
\makeindex
\newcommand{\broken}[1]{\index{#1@{\ttfamily #1}}}
\usepackage{hyperref}
\begin{document}
Hello % Remove this line and everything works.
\index{alpha@{\ttfamily alpha}} % this one is fine
\broken{lambda} % this one is broken
\printindex
\end{document}
