diff --git a/core/nginx/letsencrypt.py b/core/nginx/letsencrypt.py
index 23397d2a..9c998fe2 100755
--- a/core/nginx/letsencrypt.py
+++ b/core/nginx/letsencrypt.py
@@ -4,7 +4,7 @@ import os
 import time
 import subprocess
 
-hostnames = ','.join(set([host.strip() for host in os.environ['HOSTNAMES'].split(',')]))
+hostnames = ','.join(set(host.strip() for host in os.environ['HOSTNAMES'].split(',')))
 
 command = [
     "certbot",