diff --git a/root/etc/letsencrypt.sh/hooks_deploy_cert.d/10smeserver.sh b/root/etc/letsencrypt.sh/hooks_deploy_cert.d/10smeserver.sh
index 269b1a9..3acd658 100644
--- a/root/etc/letsencrypt.sh/hooks_deploy_cert.d/10smeserver.sh
+++ b/root/etc/letsencrypt.sh/hooks_deploy_cert.d/10smeserver.sh
@@ -6,7 +6,7 @@ KEY=${2}
 CRT=${3}
 CHAIN=${4}
 
-if [ -z $DOM -o -z $KEY -o -z $CRT -o -z $CHAIN ]; then
+if [ -z "$DOM" -o -z "$KEY" -o -z "$CRT" -o -z "$CHAIN" ]; then
   echo "Usage: $0 domain /path/to/key /path/to/cert /path/to/chain" >&2
   exit 1
 fi