diff --git a/codeforlife/tests/model_serializer.py b/codeforlife/tests/model_serializer.py
index 510141ae..6ef0e9d4 100644
--- a/codeforlife/tests/model_serializer.py
+++ b/codeforlife/tests/model_serializer.py
@@ -13,7 +13,7 @@
 from rest_framework.test import APIRequestFactory
 
 from ..serializers import ModelSerializer
-from ..types import KwArgs
+from ..types import JsonDict, KwArgs
 from ..user.models import User
 
 AnyModel = t.TypeVar("AnyModel", bound=Model)
@@ -109,7 +109,7 @@ def _assert_validate(
 
     def assert_validate(
         self,
-        attrs: t.Dict[str, t.Any],
+        attrs: t.Union[JsonDict, t.List[JsonDict]],
         error_code: str,
         user: t.Optional[User] = None,
         request_kwargs: t.Optional[KwArgs] = None,