diff --git a/acme/acme/client.py b/acme/acme/client.py
index b07009a11..46384cd85 100644
--- a/acme/acme/client.py
+++ b/acme/acme/client.py
@@ -22,7 +22,7 @@ try:
     from email.utils import parsedate_tz
 except ImportError: # pragma: no cover
     # pylint: disable=import-error,no-name-in-module
-    from email.Utils import parsedate_tz 
+    from email.Utils import parsedate_tz
 
 logger = logging.getLogger(__name__)
 
diff --git a/acme/acme/client_test.py b/acme/acme/client_test.py
index 9abc69c7c..5a43272f2 100644
--- a/acme/acme/client_test.py
+++ b/acme/acme/client_test.py
@@ -194,6 +194,10 @@ class ClientTest(unittest.TestCase):
         self.assertEqual(
             datetime.datetime(1999, 12, 31, 23, 59, 59),
             self.client.retry_after(response=self.response, default=10))
+        self.response.headers['Retry-After'] = 'Fri, 31 Dec 17 23:59:59 GMT'
+        self.assertEqual(
+            datetime.datetime(2017, 12, 31, 23, 59, 59),
+            self.client.retry_after(response=self.response, default=10))
 
     @mock.patch('acme.client.datetime')
     def test_retry_after_invalid(self, dt_mock):