diff --git a/acme/challenges_test.py b/acme/challenges_test.py
index 4c61c0e3d..f0b025ad3 100644
--- a/acme/challenges_test.py
+++ b/acme/challenges_test.py
@@ -18,6 +18,13 @@ KEY = jose.HashableRSAKey(Crypto.PublicKey.RSA.importKey(
         'acme.jose', os.path.join('testdata', 'rsa512_key.pem'))))
 
 
+class ChallengeResponseTest(unittest.TestCase):
+
+    def test_from_json_none(self):
+        from acme.challenges import ChallengeResponse
+        self.assertTrue(ChallengeResponse.from_json(None) is None)
+
+
 class SimpleHTTPTest(unittest.TestCase):
 
     def setUp(self):