diff --git a/docker-cmd.sh b/docker-cmd.sh
index 4cb55ca..6abc6fe 100755
--- a/docker-cmd.sh
+++ b/docker-cmd.sh
@@ -4,8 +4,10 @@ args=( )
 
 if [ ! -z "${HOSTNAME}" ]; then
 	args+=( "-n $HOSTNAME")
+else 
+	echo "HOSTNAME environment variable must be set."
+	exit 1
 fi
 
 python wsdd.py ${args}
 
-