diff --git a/slides_template/example.tex b/slides_template/example.tex
index e55cdfd..325b48f 100644
--- a/slides_template/example.tex
+++ b/slides_template/example.tex
@@ -8,6 +8,10 @@
 \usetheme{metropolis}
 \usepackage{appendixnumberbeamer}
 
+% math needs an OpenType math font so that every glyph carries a Unicode
+% mapping; the Computer Modern math fonts have no ToUnicode entries
+\usepackage{unicode-math}
+
 \usepackage{tagpdf}
 \tagpdfsetup{activate-all}