diff --git a/my-theorems.sty b/my-theorems.sty
index 1f2f3fbbe552a38e49b1d7d9f21d265b42f31ba3..549a2c31c58cb0ecaa568a1ebda3b34537d45a04 100644
--- a/my-theorems.sty
+++ b/my-theorems.sty
@@ -22,7 +22,7 @@
 
 % new theorems
 % check if beamer is loaded
-\ifclassloaded{beamer}{
+\@ifclassloaded{beamer}{
   \theoremstyle{definition}
   \newtheorem*{myrule}{\translate{Rule}}
   \newtheorem*{principle}{\translate{Principle}}