diff --git a/src/DependencyInjection/Configuration.php b/src/DependencyInjection/Configuration.php
index 1ddc1f651e98b6a27cd269c1dbd8ed5122b9c960..36f7340c1f9ec85944fb8c892626c76891b0a2de 100644
--- a/src/DependencyInjection/Configuration.php
+++ b/src/DependencyInjection/Configuration.php
@@ -9,7 +9,7 @@ use Symfony\Component\Config\Definition\ConfigurationInterface;
 
 class Configuration implements ConfigurationInterface
 {
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         $treeBuilder = new TreeBuilder('dbp_relay_auth');
         $treeBuilder->getRootNode()