diff --git a/src/ankisyncd/full_sync.py b/src/ankisyncd/full_sync.py
index 7050a14..a6c9b9d 100644
--- a/src/ankisyncd/full_sync.py
+++ b/src/ankisyncd/full_sync.py
@@ -23,7 +23,7 @@ class FullSyncManager:
                 "Integrity check failed for uploaded collection database file."
             )
 
-    def upload(self, col: Collection, data: bytes, session) :
+    def upload(self, col: Collection, data: bytes, session) -> str:
         """
         Uploads a sqlite database from the client to the sync server.