diff --git a/example/Makefile b/example/Makefile
index 03bf817dcdb69157bcff6c2227bb2821cc221a91..52561a323163ba8901b0167564bc2f4d85ef9700 100644
--- a/example/Makefile
+++ b/example/Makefile
@@ -6,10 +6,10 @@ presentation.pdf: diagram.pdf
 presentation.pdf: prompt.gif
 
 %.pdf: %.md
-	pandoc -t beamer $< -o $@
+	pandoc --fail-if-warnings -t beamer $< -o $@
 
 left-to-right.pdf: left-to-right.md
-	pandoc --pdf-engine=xelatex $< -o $@
+	pandoc --fail-if-warnings --pdf-engine=xelatex $< -o $@
 
 %.pdf: %.dot
 	dot $< -Tpdf > $@
diff --git a/example/presentation.md b/example/presentation.md
index 23bf6609a24f2ef82969e4434f7e5873e20e1534..f935be6304e369427ae8de40eba1c65d0b5b9ba5 100644
--- a/example/presentation.md
+++ b/example/presentation.md
@@ -17,3 +17,6 @@ author: Your name here
 ## Animated gif
 
 ![Animated gif](prompt.gif)
+
+## External image
+![External image](https://www.shore.co.il/cgit/rcfiles/plain/.face)