diff --git a/acme/messages.py b/acme/messages.py
index c224e9bde..4d82a7723 100644
--- a/acme/messages.py
+++ b/acme/messages.py
@@ -182,15 +182,27 @@ class Registration(ResourceBody):
 
     @property
     def phone(self):
-        """Phone."""
-        assert len(self.phones) == 1
-        return self.phones[0]
+        """Phone.
+
+        Picks any phone from `phones` or ``None`` if not available.
+
+        """
+        try:
+            return self.phones[0]
+        except IndexError:
+            return None
 
     @property
     def email(self):
-        """Email."""
-        assert len(self.emails) == 1
-        return self.emails[0]
+        """Email.
+
+        Picks any email from `emails` or ``None`` if not available.
+
+        """
+        try:
+            return self.emails[0]
+        except IndexError:
+            return None
 
 
 class RegistrationResource(ResourceWithURI):
diff --git a/acme/messages_test.py b/acme/messages_test.py
index 59b1685dc..4f99b538d 100644
--- a/acme/messages_test.py
+++ b/acme/messages_test.py
@@ -122,6 +122,7 @@ class RegistrationTest(unittest.TestCase):
         self.reg = Registration(
             key=key, contact=contact, recovery_token=recovery_token,
             agreement=agreement)
+        self.reg_none = Registration()
 
         self.jobj_to = {
             'contact': contact,
@@ -149,9 +150,15 @@ class RegistrationTest(unittest.TestCase):
     def test_phone(self):
         self.assertEqual('1234', self.reg.phone)
 
+    def test_phone_none(self):
+        self.assertTrue(self.reg_none.phone is None)
+
     def test_email(self):
         self.assertEqual('admin@foo.com', self.reg.email)
 
+    def test_email_none(self):
+        self.assertTrue(self.reg_none.email is None)
+
     def test_to_partial_json(self):
         self.assertEqual(self.jobj_to, self.reg.to_partial_json())