diff --git a/lib/Service/Index.php b/lib/Service/Index.php
index bf95b4ee7..bfb9a7926 100644
--- a/lib/Service/Index.php
+++ b/lib/Service/Index.php
@@ -182,7 +182,7 @@ public function indexFolder(Folder $folder): void
             $addFilter('memories_failures', 'fail', false);
 
             // Get file IDs to actually index
-            $fileIds = Util::transaction(static fn () => $query->executeQuery()->fetchAll(\PDO::FETCH_COLUMN));
+            $fileIds = Util::transaction(static fn (): array => $query->executeQuery()->fetchAll(\PDO::FETCH_COLUMN));
 
             // Index files
             foreach ($fileIds as $fileId) {