diff --git a/2019/karns/demo.sh b/2019/karns/demo.sh
index 1ed349763..e70d0f521 100755
--- a/2019/karns/demo.sh
+++ b/2019/karns/demo.sh
@@ -5,6 +5,9 @@
 # Doesn't run the program on README.md as it's longer and slower.
 #
 
+# make prog first and exit if failure
+make || exit
+
 # display prog.c to the user
 echo "$ cat prog.c"
 cat prog.c