diff --git a/server/mergin/sync/utils.py b/server/mergin/sync/utils.py
index e8c9f367..72426d01 100644
--- a/server/mergin/sync/utils.py
+++ b/server/mergin/sync/utils.py
@@ -336,4 +336,4 @@ def files_size():
         SELECT pg_size_pretty(SUM(sum)) FROM partials;
         """
     )
-    return db.session.execute(files_size).scalar()
+    return db.session.execute(files_size).scalar() or "0 bytes"