diff --git a/tests/lib/TagsTest.php b/tests/lib/TagsTest.php
index ea531bd939f6e..4aeaeeed86eb4 100644
--- a/tests/lib/TagsTest.php
+++ b/tests/lib/TagsTest.php
@@ -38,6 +38,7 @@ class TagsTest extends \Test\TestCase {
 	protected $tagMapper;
 	/** @var ITagManager */
 	protected $tagMgr;
+	protected IRootFolder $rootFolder;
 
 	protected function setUp(): void {
 		parent::setUp();