diff --git a/tests/custom_bootstrap.php b/tests/custom_bootstrap.php
index c392890e9..073116ba2 100644
--- a/tests/custom_bootstrap.php
+++ b/tests/custom_bootstrap.php
@@ -17,7 +17,7 @@
 use Symfony\Component\Console\Output\NullOutput;
 use Symfony\Component\Filesystem\Filesystem;
 
-$kernel = new AppKernel($_SERVER['APP_ENV'], (bool) $_SERVER['APP_DEBUG']);
+$kernel = new AppKernel($_SERVER['APP_ENV'] ?? 'test', (bool) ($_SERVER['APP_DEBUG'] ?? false));
 $application = new Application($kernel);
 $application->setAutoExit(false);