diff --git a/acme/acme/client.py b/acme/acme/client.py
index eaca6dc7d..79d7c5df4 100644
--- a/acme/acme/client.py
+++ b/acme/acme/client.py
@@ -4,6 +4,7 @@ import datetime
 import heapq
 import logging
 import time
+from email.utils import parsedate_tz
 
 import six
 from six.moves import http_client  # pylint: disable=import-error
@@ -17,7 +18,6 @@ from acme import jose
 from acme import jws
 from acme import messages
 
-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 29f60c25d..93c86862d 100644
--- a/acme/acme/client_test.py
+++ b/acme/acme/client_test.py
@@ -205,8 +205,12 @@ class ClientTest(unittest.TestCase):
             datetime.datetime(2015, 3, 27, 0, 0, 10),
             self.client.retry_after(response=self.response, default=10))
 
-        # wrong date -> ValueError
+    @mock.patch('acme.client.datetime')
+    def test_retry_after_overflow(self, dt_mock):
+        dt_mock.datetime.now.return_value = datetime.datetime(2015, 3, 27)
+        dt_mock.timedelta = datetime.timedelta
         dt_mock.datetime.side_effect = datetime.datetime
+
         self.response.headers['Retry-After'] = "Tue, 116 Feb 2016 11:50:00 MST"
         self.assertEqual(
             datetime.datetime(2015, 3, 27, 0, 0, 10),