diff --git a/src/Tests/ApplicationHelper.php b/src/Tests/ApplicationHelper.php
index b5d762a..e7da58b 100644
--- a/src/Tests/ApplicationHelper.php
+++ b/src/Tests/ApplicationHelper.php
@@ -51,6 +51,10 @@ trait ApplicationHelper
     #[\PHPUnit\Framework\Attributes\BeforeClass]
     public static function loadApplication(): void
     {
+        // This avoids to register extensions multiple times (normally done in
+        // the Application class constructor) as it would fail.
+        \Minz\Template\Twig::reset();
+
         $app_name = \Minz\Configuration::$app_name;
         $application_class_name = "\\{$app_name}\\Application";
         try {