diff --git a/includes/ServiceWiring.php b/includes/ServiceWiring.php
index da55b85b..095bf939 100644
--- a/includes/ServiceWiring.php
+++ b/includes/ServiceWiring.php
@@ -31,7 +31,7 @@ use MediaWiki\MediaWikiServices;
  * CategoryTree wiring for MediaWiki services.
  */
 return [
-	'CategoryTree.CategoryCache' => static function ( MediaWikiServices $services ) {
+	'CategoryTree.CategoryCache' => static function ( MediaWikiServices $services ): CategoryCache {
 		return new CategoryCache(
 			$services->getDBLoadBalancer()
 		);