diff --git a/requests/utils.py b/requests/utils.py
index 2c6bb090..539a68a0 100644
--- a/requests/utils.py
+++ b/requests/utils.py
@@ -555,7 +555,7 @@ def default_headers():
         'User-Agent': default_user_agent(),
         'Accept-Encoding': ', '.join(('gzip', 'deflate')),
         'Accept': '*/*',
-        'Connection': 'keep-alive'
+        'Connection': 'keep-alive',
     })