diff --git a/src/Bundle/DependencyInjection/Configuration.php b/src/Bundle/DependencyInjection/Configuration.php
index 2dcd2d3..a22fe25 100755
--- a/src/Bundle/DependencyInjection/Configuration.php
+++ b/src/Bundle/DependencyInjection/Configuration.php
@@ -9,7 +9,7 @@
 
 class Configuration implements ConfigurationInterface
 {
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         $treeBuilder = new TreeBuilder('sourceability_instrumentation');
         $rootNode = $treeBuilder->getRootNode();