diff --git a/letsencrypt/client/le_util.py b/letsencrypt/client/le_util.py
index 31edfd13b..8a87d7c09 100644
--- a/letsencrypt/client/le_util.py
+++ b/letsencrypt/client/le_util.py
@@ -97,7 +97,7 @@ def jose_b64decode(arg, decoding='utf-8'):
     """JOSE Base64 decode.
 
     :param arg: Base64 string to be decoded.
-    :type arg: str
+    :type arg: str or unicode
 
     :param decoding: Name of the encoding to be performed after
                      Base64 decoding.
@@ -107,5 +107,6 @@ def jose_b64decode(arg, decoding='utf-8'):
     :rtype: str or unicode
 
     """
-    decoded = base64.urlsafe_b64decode(arg + '=' * (4 - (len(arg) % 4)))
+    ascii = arg.encode('ascii')  # equivalent to str(arg), for unicode input
+    decoded = base64.urlsafe_b64decode(ascii + '=' * (4 - (len(ascii) % 4)))
     return decoded if decoding is None else decoded.decode(decoding)
diff --git a/letsencrypt/client/le_util_test.py b/letsencrypt/client/le_util_test.py
index 7f8bc8c58..6c2714a8d 100644
--- a/letsencrypt/client/le_util_test.py
+++ b/letsencrypt/client/le_util_test.py
@@ -126,6 +126,9 @@ class JOSEB64DecodeTest(unittest.TestCase):
     def test_with_encoding(self):
         self.assertEqual(self._call('xIU=', 'utf-8'), u'\u0105')
 
+    def test_unicode(self):
+        self.assertEqual(self._call(u'YQ', None), 'a')
+
 
 if __name__ == '__main__':
     unittest.main()