diff --git a/cours/cours_beamer.cls b/cours/cours_beamer.cls
index 6d8d709..ae7d7d6 100644
--- a/cours/cours_beamer.cls
+++ b/cours/cours_beamer.cls
@@ -42,7 +42,7 @@
 \usetheme{Madrid}
 \useinnertheme{circles}
 \useoutertheme{default}
-\usefonttheme{serif}
+\usefonttheme[onlymath]{serif}
 
 % enumerate
 \setbeamerfont{enumerate item}{family=\rmfamily}