diff --git a/little_boxes/activitypub.py b/little_boxes/activitypub.py
index 269d9f6..59c9f3b 100644
--- a/little_boxes/activitypub.py
+++ b/little_boxes/activitypub.py
@@ -797,10 +797,7 @@ class Announce(BaseActivity):
         BACKEND.outbox_undo_announce(as_actor, self)
 
     def build_undo(self) -> BaseActivity:
-        return Undo(
-            actor=self.get_actor().id,
-            object=self.to_dict(embed=True),
-        )
+        return Undo(actor=self.get_actor().id, object=self.to_dict(embed=True))
 
 
 class Delete(BaseActivity):
diff --git a/little_boxes/backend.py b/little_boxes/backend.py
index 7db6f40..84e7879 100644
--- a/little_boxes/backend.py
+++ b/little_boxes/backend.py
@@ -83,7 +83,9 @@ class Backend(abc.ABC):
         pass
 
     @abc.abstractmethod
-    def inbox_undo_announce(self, as_actor: "ap.Person", activity: "ap.Announce") -> None:
+    def inbox_undo_announce(
+        self, as_actor: "ap.Person", activity: "ap.Announce"
+    ) -> None:
         pass
 
     @abc.abstractmethod