diff --git a/etebase_fastapi/collection.py b/etebase_fastapi/collection.py
index 3af5af0..6757ac3 100644
--- a/etebase_fastapi/collection.py
+++ b/etebase_fastapi/collection.py
@@ -31,10 +31,7 @@ class CollectionItemRevisionInOut(BaseModel):
     uid: str
     meta: bytes
     deleted: bool
-    chunks: t.List[t.Union[
-        t.Tuple[str],
-        t.Tuple[str, bytes],
-        ]]
+    chunks: t.List[t.Tuple[str, t.Optional[bytes]]]
 
     class Config:
         orm_mode = True