diff --git a/borg/helpers.py b/borg/helpers.py
index 62b327816..57f0a7022 100644
--- a/borg/helpers.py
+++ b/borg/helpers.py
@@ -462,7 +462,7 @@ def dir_is_tagged(path, exclude_caches, exclude_if_present):
 def format_time(t):
     """use ISO-8601 date and time format
     """
-    return t.strftime('%Y-%m-%d %H:%M:%S')
+    return t.strftime('%a, %Y-%m-%d %H:%M:%S')
 
 
 def format_timedelta(td):