diff --git a/evoacme/files/evoacme.sh b/evoacme/files/evoacme.sh
index 1b2c060d..49947b33 100755
--- a/evoacme/files/evoacme.sh
+++ b/evoacme/files/evoacme.sh
@@ -8,6 +8,7 @@
 #
 
 set -e
+set -u
 
 usage() {
     echo "Usage: $0 [ --cron ] NAME"