diff --git a/README.md b/README.md
index 18b8f35..ed97e39 100644
--- a/README.md
+++ b/README.md
@@ -62,6 +62,19 @@ FriendsOfBehat\SymfonyExtension:
         debug: true  # When explicitly set, will override APP_DEBUG loaded from env_file file
 ```
 
-Symfony 4 is detected, based on the existence of `src/Kernel.php` file, so if you did not migrate to new Symfony structure yet; you need to set those values yourself.
+Symfony 4 is automatically detected, based on the existence of default `src/Kernel.php` kernel file.
+
+If you did not migrate to new Symfony structure yet or you are using custom paths/naming; you need to configure `kernel.boostrap` parameter, to enable default Symfony 4 configuration as shown in the example below:
+
+```
+FriendsOfBehat\SymfonyExtension:
+    # env_file: .env # loaded from the default configuration
+    kernel:
+        bootstrap: ~ # this enables default Symfony 4 configuration
+        path: app/AppKernel.php
+        # class: 'App\Kernel' # loaded from the default configuration
+        # env: test # loaded from the default configuration
+        # debug: true  # loaded from the default configuration
+```
 
 Of course, you can always change each of those settings.
diff --git a/features/not_crashing_behat.feature b/features/not_crashing_behat.feature
index 69f0135..a2e0f7b 100644
--- a/features/not_crashing_behat.feature
+++ b/features/not_crashing_behat.feature
@@ -8,9 +8,12 @@ Feature: Not crashing Behat
         """
         default:
             extensions:
-                FriendsOfBehat\SymfonyExtension:
-                    kernel:
-                        bootstrap: ~
+                FriendsOfBehat\SymfonyExtension: ~
+        """
+        And a file "app/autoload.php" containing:
+        """
+        <?php
+
         """
         And a file "app/AppKernel.php" containing:
         """
@@ -36,11 +39,16 @@ Feature: Not crashing Behat
             extensions:
                 FriendsOfBehat\SymfonyExtension:
                     kernel:
-                        bootstrap: ~
+                        bootstrap: app/autoload.php
                         path: app/MyKernel.php
                         class: MyKernel
                         env: test
                         debug: true
+        """
+        And a file "app/autoload.php" containing:
+        """
+        <?php
+
         """
         And a file "app/MyKernel.php" containing:
         """
@@ -163,11 +171,13 @@ Feature: Not crashing Behat
         """
         default:
             extensions:
-                FriendsOfBehat\SymfonyExtension:
-                    kernel:
-                        bootstrap: ~
-
+                FriendsOfBehat\SymfonyExtension: ~
                 FriendsOfBehat\CrossContainerExtension: ~
+        """
+        And a file "app/autoload.php" containing:
+        """
+        <?php
+
         """
         And a file "app/AppKernel.php" containing:
         """
diff --git a/src/ServiceContainer/SymfonyExtension.php b/src/ServiceContainer/SymfonyExtension.php
index 87ee0f7..91230ad 100644
--- a/src/ServiceContainer/SymfonyExtension.php
+++ b/src/ServiceContainer/SymfonyExtension.php
@@ -122,8 +122,9 @@ final class SymfonyExtension implements Extension
             ->children()
                 ->scalarNode('env_file')->end()
                 ->arrayNode('kernel')
+                    ->addDefaultsIfNotSet()
                     ->children()
-                        ->scalarNode('bootstrap')->end()
+                        ->scalarNode('bootstrap')->defaultFalse()->end()
                         ->scalarNode('path')->end()
                         ->scalarNode('class')->end()
                         ->scalarNode('env')->end()
@@ -165,15 +166,17 @@ final class SymfonyExtension implements Extension
      * @param array $userConfig
      * @return array
      */
-    private function autoconfigure(ContainerBuilder $container, array $userConfig) {
-
+    private function autoconfigure(ContainerBuilder $container, array $userConfig): array
+    {
         $defaults = self::SYMFONY_DEFAULTS;
 
-        $symfony4KernelPath = sprintf('%s/%s', $container->getParameter('paths.base'), self::SYMFONY_4_DEFAULTS['kernel']['path']);
-        if (file_exists($symfony4KernelPath)) {
+        $symfonyFourKernelPath = sprintf('%s/%s', $container->getParameter('paths.base'), self::SYMFONY_4_DEFAULTS['kernel']['path']);
+        if ($userConfig['kernel']['bootstrap'] === null || file_exists($symfonyFourKernelPath)) {
             $defaults = self::SYMFONY_4_DEFAULTS;
         }
 
+        $userConfig['kernel']['bootstrap'] = $userConfig['kernel']['bootstrap'] === false ? null : $userConfig['kernel']['bootstrap'];
+
         $config = array_replace_recursive($defaults, $userConfig);
 
         if (null !== $config['env_file']) {