diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..6802f22
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,5 @@
+parameters:
+    reportUnmatchedIgnoredErrors: false
+
+    ignoreErrors:
+        - '/Cannot call method [a-zA-Z0-9]+\(\) on Symfony\\Component\\Config\\Definition\\Builder\\NodeParentInterface|null\./'
diff --git a/src/Driver/SymfonyDriver.php b/src/Driver/SymfonyDriver.php
index 6556902..de0267b 100644
--- a/src/Driver/SymfonyDriver.php
+++ b/src/Driver/SymfonyDriver.php
@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace FriendsOfBehat\SymfonyExtension\Driver;
 
 use Behat\Mink\Driver\BrowserKitDriver;
+use Symfony\Component\BrowserKit\Client;
 use Symfony\Component\HttpKernel\KernelInterface;
 
 final class SymfonyDriver extends BrowserKitDriver
@@ -15,6 +16,16 @@ final class SymfonyDriver extends BrowserKitDriver
      */
     public function __construct(KernelInterface $kernel, string $baseUrl)
     {
-        parent::__construct($kernel->getContainer()->get('test.client'), $baseUrl);
+        $testClient = $kernel->getContainer()->get('test.client');
+
+        if (!$testClient instanceof Client) {
+            throw new \RuntimeException(sprintf(
+                'Expected service "test.client" to be an instance of "%s", got "%s" instead.',
+                Client::class,
+                \is_object($testClient) ? \get_class($testClient) : \gettype($testClient)
+            ));
+        }
+
+        parent::__construct($testClient, $baseUrl);
     }
 }
diff --git a/src/ServiceContainer/SymfonyExtension.php b/src/ServiceContainer/SymfonyExtension.php
index f596a8b..873a4f7 100644
--- a/src/ServiceContainer/SymfonyExtension.php
+++ b/src/ServiceContainer/SymfonyExtension.php
@@ -19,6 +19,7 @@ use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Definition;
 use Symfony\Component\DependencyInjection\Reference;
 use Symfony\Component\Dotenv\Dotenv;
+use Symfony\Component\HttpKernel\KernelInterface;
 
 final class SymfonyExtension implements Extension
 {
@@ -162,9 +163,13 @@ final class SymfonyExtension implements Extension
             $config['debug'],
         ]);
         $definition->addMethodCall('boot');
-        $definition->setFile($this->getKernelFile($container->getParameter('paths.base'), $config['path']));
         $definition->setPublic(true);
 
+        $file = $this->getKernelFile($container->getParameter('paths.base'), $config['path']);
+        if (null !== $file) {
+            $definition->setFile($file);
+        }
+
         $container->setDefinition(self::KERNEL_ID, $definition);
 
         $this->requireKernelBootstrapFile($container->getParameter('paths.base'), $config['bootstrap']);
@@ -221,7 +226,7 @@ final class SymfonyExtension implements Extension
      */
     private function loadKernelRebooter(ContainerBuilder $container): void
     {
-        $definition = new Definition(KernelRebooter::class, [$container->get(self::KERNEL_ID)]);
+        $definition = new Definition(KernelRebooter::class, [new Reference(self::KERNEL_ID)]);
         $definition->addTag(EventDispatcherExtension::SUBSCRIBER_TAG);
 
         $container->setDefinition(self::KERNEL_ID . '.rebooter', $definition);
@@ -234,21 +239,29 @@ final class SymfonyExtension implements Extension
      */
     private function declareSymfonyContainers(ContainerBuilder $container): void
     {
-        if (null !== $this->crossContainerProcessor) {
-            $this->crossContainerProcessor->addContainerAccessor(
-                'symfony',
-                new KernelBasedContainerAccessor($container->get(self::KERNEL_ID))
-            );
+        if (null === $this->crossContainerProcessor) {
+            return;
+        }
 
-            $this->crossContainerProcessor->addContainerAccessor(
-                'symfony_driver',
-                new KernelBasedContainerAccessor($container->get(self::DRIVER_KERNEL_ID))
-            );
+        $containerAccessors = [
+            'symfony' => self::KERNEL_ID,
+            'symfony_driver' => self::DRIVER_KERNEL_ID,
+            'symfony_shared' => self::SHARED_KERNEL_ID,
+        ];
 
-            $this->crossContainerProcessor->addContainerAccessor(
-                'symfony_shared',
-                new KernelBasedContainerAccessor($container->get(self::SHARED_KERNEL_ID))
-            );
+        foreach ($containerAccessors as $containerName => $kernelIdentifier) {
+            $kernel = $container->get($kernelIdentifier);
+
+            if (!$kernel instanceof KernelInterface) {
+                throw new \RuntimeException(sprintf(
+                    'Expected service "%s" to be an instance of "%s", got "%s" instead.',
+                    $kernelIdentifier,
+                    KernelInterface::class,
+                    \is_object($kernel) ? \get_class($kernel) : \gettype($kernel)
+                ));
+            }
+
+            $this->crossContainerProcessor->addContainerAccessor($containerName, new KernelBasedContainerAccessor($kernel));
         }
     }
 
@@ -269,7 +282,7 @@ final class SymfonyExtension implements Extension
      */
     private function registerSymfonyDriverFactory(ExtensionManager $extensionManager): void
     {
-        /** @var MinkExtension $minkExtension */
+        /** @var MinkExtension|null $minkExtension */
         $minkExtension = $extensionManager->getExtension('mink');
         if (null === $minkExtension) {
             return;