diff --git a/update-zonefile.py b/update-zonefile.py
index f2094fb..0f08508 100755
--- a/update-zonefile.py
+++ b/update-zonefile.py
@@ -24,7 +24,7 @@
 
 import requests
 from pathlib import Path
-from datetime import datetime
+from datetime import datetime, timezone
 import email.utils as eut
 import os
 import hashlib
@@ -67,7 +67,7 @@ def download_list(url):
     cache = Path(config['cache'], hashlib.sha1(url.encode()).hexdigest())
 
     if cache.is_file():
-        last_modified = datetime.utcfromtimestamp(cache.stat().st_mtime)
+        last_modified = datetime.fromtimestamp(cache.stat().st_mtime, tz=timezone.utc)
         headers = {
                 'If-modified-since': eut.format_datetime(last_modified),
                 'User-Agent': 'Bind adblock zonfile updater v1.0 (https://github.com/Trellmor/bind-adblock)'