diff --git a/backend/btrixcloud/colls.py b/backend/btrixcloud/colls.py
index 7e398ceaa..22ad1e8d3 100644
--- a/backend/btrixcloud/colls.py
+++ b/backend/btrixcloud/colls.py
@@ -608,9 +608,13 @@ async def stream_iter():
                     f"Unable to delete previous collection thumbnail: {coll.thumbnail.filename}"
                 )
 
+        coll.thumbnail = thumbnail_file
+
+        # Update entire document to avoid bson.errors.InvalidDocument error
+        # with thumbnail
         await self.collections.find_one_and_update(
             {"_id": coll_id, "oid": org.id},
-            {"$set": {"thumbnail": dict(thumbnail_file)}},
+            {"$set": coll.to_dict()},
         )
 
         return {"added": True}