diff --git a/make-includes/build_lecture_rules.make b/make-includes/build_lecture_rules.make
index 556cda8..3ac3da0 100644
--- a/make-includes/build_lecture_rules.make
+++ b/make-includes/build_lecture_rules.make
@@ -48,7 +48,7 @@
 # Important: default font size for Beamer is 11pt. We need to define this before
 # loading the standard environment. However, allow the user to override it!
 ifndef FONT_SIZE
-FONT_SIZE=11pt
+FONT_SIZE=
 endif
 
 include $(GLOBAL_HANDBOOK_INCLUDE)/standard_environment.make