diff --git a/eZ/Bundle/EzPublishDebugBundle/Twig/DebugTemplate.php b/eZ/Bundle/EzPublishDebugBundle/Twig/DebugTemplate.php
index 313386a7f9..b0116dd091 100644
--- a/eZ/Bundle/EzPublishDebugBundle/Twig/DebugTemplate.php
+++ b/eZ/Bundle/EzPublishDebugBundle/Twig/DebugTemplate.php
@@ -19,7 +19,7 @@ class DebugTemplate extends Template
 {
     private $fileSystem;
 
-    public function display(array $context, array $blocks = [])
+    public function display(array $context, array $blocks = []): void
     {
         $this->fileSystem = $this->fileSystem ?: new Filesystem();