diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index bf688b8..6dfa801 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -20,7 +20,7 @@ class Configuration implements ConfigurationInterface
      *
      * @return TreeBuilder The tree builder
      */
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         $treeBuilder = new TreeBuilder('avro_case');
         $rootNode = method_exists(TreeBuilder::class, 'getRootNode') ? $treeBuilder->getRootNode() : $treeBuilder->root('avro_case');