diff --git a/bookwyrm/activitypub/base_activity.py b/bookwyrm/activitypub/base_activity.py
index f7f4b216c..05e7d8a05 100644
--- a/bookwyrm/activitypub/base_activity.py
+++ b/bookwyrm/activitypub/base_activity.py
@@ -1,4 +1,5 @@
 """ basics for an activitypub serializer """
+from __future__ import annotations
 from dataclasses import dataclass, fields, MISSING
 from json import JSONEncoder
 import logging
@@ -72,7 +73,9 @@ class ActivityObject:
 
     def __init__(
         self,
-        activity_objects: Optional[list[str, base_model.BookWyrmModel]] = None,
+        activity_objects: Optional[
+            dict[str, Union[str, list[str], ActivityObject, base_model.BookWyrmModel]]
+        ] = None,
         **kwargs: Any,
     ):
         """this lets you pass in an object with fields that aren't in the
diff --git a/bookwyrm/utils/cache.py b/bookwyrm/utils/cache.py
index 5e896e621..c8262ef59 100644
--- a/bookwyrm/utils/cache.py
+++ b/bookwyrm/utils/cache.py
@@ -6,12 +6,12 @@ from django.core.cache import cache
 
 def get_or_set(
     cache_key: str,
-    function: Callable[..., Any],
+    function: Callable[..., str],
     *args: Tuple[Any, ...],
     timeout: Union[float, None] = None
-) -> Any:
+) -> str:
     """Django's built-in get_or_set isn't cutting it"""
-    value = cache.get(cache_key)
+    value = str(cache.get(cache_key))
     if value is None:
         value = function(*args)
         cache.set(cache_key, value, timeout=timeout)