diff --git a/etebase_fastapi/collection.py b/etebase_fastapi/collection.py
index 3e4d3e8..5c6e6b6 100644
--- a/etebase_fastapi/collection.py
+++ b/etebase_fastapi/collection.py
@@ -88,7 +88,8 @@ class CollectionItemIn(CollectionItemCommon):
 
 
 class CollectionCommon(BaseModel):
-    collectionType: bytes
+    # FIXME: remove optional once we finish collection-type-migration
+    collectionType: t.Optional[bytes]
     collectionKey: bytes