diff --git a/bookwyrm/models/base_model.py b/bookwyrm/models/base_model.py
index 94fbc015..d3c9471f 100644
--- a/bookwyrm/models/base_model.py
+++ b/bookwyrm/models/base_model.py
@@ -142,10 +142,10 @@ class ActivitypubMixin:
     def to_undo_activity(self, user):
         ''' undo an action '''
         return activitypub.Undo(
-            id='%s#undo' % user.remote_id,
+            id='%s#undo' % self.remote_id,
             actor=user.remote_id,
             object=self.to_activity()
-        )
+        ).serialize()
 
 
 class OrderedCollectionPageMixin(ActivitypubMixin):
diff --git a/bookwyrm/tests/models/test_base_model.py b/bookwyrm/tests/models/test_base_model.py
index 40306d91..b187284a 100644
--- a/bookwyrm/tests/models/test_base_model.py
+++ b/bookwyrm/tests/models/test_base_model.py
@@ -105,7 +105,6 @@ class BaseModel(TestCase):
             lambda *args: {}
         )
         activity = ActivitypubMixin.to_update_activity(mock_self, user)
-        print(activity['id'])
         self.assertIsNotNone(
             re.match(
                 r'^https:\/\/example\.com\/status\/1#update\/.*',
@@ -118,3 +117,21 @@ class BaseModel(TestCase):
             activity['to'],
             ['https://www.w3.org/ns/activitystreams#Public'])
         self.assertEqual(activity['object'], {})
+
+    def test_to_undo_activity(self):
+        user = models.User.objects.create_user(
+            'mouse', 'mouse@mouse.com', 'mouseword', local=True)
+
+        MockSelf = namedtuple('Self', ('remote_id', 'to_activity'))
+        mock_self = MockSelf(
+            'https://example.com/status/1',
+            lambda *args: {}
+        )
+        activity = ActivitypubMixin.to_undo_activity(mock_self, user)
+        self.assertEqual(
+            activity['id'],
+            'https://example.com/status/1#undo'
+        )
+        self.assertEqual(activity['actor'], user.remote_id)
+        self.assertEqual(activity['type'], 'Undo')
+        self.assertEqual(activity['object'], {})