diff --git a/.travis.yml b/.travis.yml
index f4a0a60..9812240 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,17 +2,9 @@ language: php
 
 php:
     - 7.1
-    - 7.0
-    - 5.6
-
-env:
-    global:
-        - COMPOSER_OPTIONS=""
 
 matrix:
     include:
-        - php: 5.6
-          env: COMPOSER_OPTIONS="--prefer-lowest"
         - php: nightly
     allow_failures:
         - php: nightly
@@ -26,7 +18,7 @@ before_install:
     - phpenv config-rm xdebug.ini || true
 
 install:
-    - composer update --prefer-dist $COMPOSER_OPTIONS
+    - composer update --prefer-dist
 
 script:
     - composer validate --strict
diff --git a/composer.json b/composer.json
index 4fa2478..c9c74ef 100644
--- a/composer.json
+++ b/composer.json
@@ -10,7 +10,7 @@
         }
     ],
     "require": {
-        "php": "^5.6|^7.0",
+        "php": "^7.1",
 
         "behat/behat": "^3.1",
         "symfony/http-kernel": "^2.7|^3.0"
diff --git a/src/Driver/Factory/SymfonyDriverFactory.php b/src/Driver/Factory/SymfonyDriverFactory.php
index 6921f70..dac8de9 100644
--- a/src/Driver/Factory/SymfonyDriverFactory.php
+++ b/src/Driver/Factory/SymfonyDriverFactory.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /*
  * This file is part of the SymfonyExtension package.
  *
@@ -33,7 +35,7 @@ final class SymfonyDriverFactory implements DriverFactory
      * @param string $name
      * @param Reference $kernel
      */
-    public function __construct($name, Reference $kernel)
+    public function __construct(string $name, Reference $kernel)
     {
         $this->name = $name;
         $this->kernel = $kernel;
@@ -42,7 +44,7 @@ final class SymfonyDriverFactory implements DriverFactory
     /**
      * {@inheritdoc}
      */
-    public function getDriverName()
+    public function getDriverName(): string
     {
         return $this->name;
     }
@@ -50,7 +52,7 @@ final class SymfonyDriverFactory implements DriverFactory
     /**
      * {@inheritdoc}
      */
-    public function supportsJavascript()
+    public function supportsJavascript(): bool
     {
         return false;
     }
@@ -58,7 +60,7 @@ final class SymfonyDriverFactory implements DriverFactory
     /**
      * {@inheritdoc}
      */
-    public function configure(ArrayNodeDefinition $builder)
+    public function configure(ArrayNodeDefinition $builder): void
     {
 
     }
@@ -66,7 +68,7 @@ final class SymfonyDriverFactory implements DriverFactory
     /**
      * {@inheritdoc}
      */
-    public function buildDriver(array $config)
+    public function buildDriver(array $config): Definition
     {
         return new Definition(SymfonyDriver::class, [
             $this->kernel,
diff --git a/src/Driver/SymfonyDriver.php b/src/Driver/SymfonyDriver.php
index 3368c2d..c772a9a 100644
--- a/src/Driver/SymfonyDriver.php
+++ b/src/Driver/SymfonyDriver.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /*
  * This file is part of the SymfonyExtension package.
  *
@@ -20,7 +22,7 @@ final class SymfonyDriver extends BrowserKitDriver
      * @param KernelInterface $kernel
      * @param string $baseUrl
      */
-    public function __construct(KernelInterface $kernel, $baseUrl)
+    public function __construct(KernelInterface $kernel, string $baseUrl)
     {
         parent::__construct($kernel->getContainer()->get('test.client'), $baseUrl);
     }
diff --git a/src/Listener/KernelRebooter.php b/src/Listener/KernelRebooter.php
index cc2b2c1..d68825f 100644
--- a/src/Listener/KernelRebooter.php
+++ b/src/Listener/KernelRebooter.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /*
  * This file is part of the SymfonyExtension package.
  *
@@ -34,7 +36,7 @@ final class KernelRebooter implements EventSubscriberInterface
     /**
      * {@inheritdoc}
      */
-    public static function getSubscribedEvents()
+    public static function getSubscribedEvents(): array
     {
         return [
             ScenarioTested::AFTER => ['rebootKernel', -15],
@@ -42,7 +44,7 @@ final class KernelRebooter implements EventSubscriberInterface
         ];
     }
 
-    public function rebootKernel()
+    public function rebootKernel(): void
     {
         $this->kernel->shutdown();
         $this->kernel->boot();
diff --git a/src/ServiceContainer/SymfonyExtension.php b/src/ServiceContainer/SymfonyExtension.php
index 0e9cb89..7eb8b60 100644
--- a/src/ServiceContainer/SymfonyExtension.php
+++ b/src/ServiceContainer/SymfonyExtension.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /*
  * This file is part of the SymfonyExtension package.
  *
@@ -67,7 +69,7 @@ final class SymfonyExtension implements Extension
     /**
      * {@inheritdoc}
      */
-    public function getConfigKey()
+    public function getConfigKey(): string
     {
         return 'fob_symfony';
     }
@@ -75,7 +77,7 @@ final class SymfonyExtension implements Extension
     /**
      * {@inheritdoc}
      */
-    public function initialize(ExtensionManager $extensionManager)
+    public function initialize(ExtensionManager $extensionManager): void
     {
         $this->registerSymfonyDriverFactory($extensionManager);
         $this->initializeCrossContainerProcessor($extensionManager);
@@ -84,7 +86,7 @@ final class SymfonyExtension implements Extension
     /**
      * {@inheritdoc}
      */
-    public function configure(ArrayNodeDefinition $builder)
+    public function configure(ArrayNodeDefinition $builder): void
     {
         $builder
             ->addDefaultsIfNotSet()
@@ -97,13 +99,17 @@ final class SymfonyExtension implements Extension
                             ->scalarNode('class')->defaultValue('AppKernel')->end()
                             ->scalarNode('env')->defaultValue('test')->end()
                             ->booleanNode('debug')->defaultTrue()->end()
+                        ->end()
+                    ->end()
+                ->end()
+            ->end()
         ;
     }
 
     /**
      * {@inheritdoc}
      */
-    public function load(ContainerBuilder $container, array $config)
+    public function load(ContainerBuilder $container, array $config): void
     {
         $this->loadKernel($container, $config['kernel']);
         $this->loadKernelContainer($container);
@@ -120,14 +126,14 @@ final class SymfonyExtension implements Extension
     /**
      * {@inheritdoc}
      */
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
     }
 
     /**
      * @param ContainerBuilder $container
      */
-    private function loadKernel(ContainerBuilder $container, array $config)
+    private function loadKernel(ContainerBuilder $container, array $config): void
     {
         $definition = new Definition($config['class'], array(
             $config['env'],
@@ -144,7 +150,7 @@ final class SymfonyExtension implements Extension
     /**
      * @param ContainerBuilder $container
      */
-    private function loadKernelContainer(ContainerBuilder $container)
+    private function loadKernelContainer(ContainerBuilder $container): void
     {
         $containerDefinition = new Definition(Container::class);
         $containerDefinition->setFactory([
@@ -158,7 +164,7 @@ final class SymfonyExtension implements Extension
     /**
      * @param ContainerBuilder $container
      */
-    private function loadDriverKernel(ContainerBuilder $container)
+    private function loadDriverKernel(ContainerBuilder $container): void
     {
         $container->setDefinition(self::DRIVER_KERNEL_ID, $container->findDefinition(self::KERNEL_ID));
     }
@@ -166,7 +172,7 @@ final class SymfonyExtension implements Extension
     /**
      * @param ContainerBuilder $container
      */
-    private function loadSharedKernel(ContainerBuilder $container)
+    private function loadSharedKernel(ContainerBuilder $container): void
     {
         $container->setDefinition(self::SHARED_KERNEL_ID, $container->findDefinition(self::KERNEL_ID));
     }
@@ -174,7 +180,7 @@ final class SymfonyExtension implements Extension
     /**
      * @param ContainerBuilder $container
      */
-    private function loadSharedKernelContainer(ContainerBuilder $container)
+    private function loadSharedKernelContainer(ContainerBuilder $container): void
     {
         $containerDefinition = new Definition(Container::class);
         $containerDefinition->setFactory([
@@ -188,7 +194,7 @@ final class SymfonyExtension implements Extension
     /**
      * @param ContainerBuilder $container
      */
-    private function loadKernelRebooter(ContainerBuilder $container)
+    private function loadKernelRebooter(ContainerBuilder $container): void
     {
         $definition = new Definition(KernelRebooter::class, [new Reference(self::KERNEL_ID)]);
         $definition->addTag(EventDispatcherExtension::SUBSCRIBER_TAG);
@@ -199,7 +205,7 @@ final class SymfonyExtension implements Extension
     /**
      * @param ContainerBuilder $container
      */
-    private function declareSymfonyContainers(ContainerBuilder $container)
+    private function declareSymfonyContainers(ContainerBuilder $container): void
     {
         if (null !== $this->crossContainerProcessor) {
             $this->crossContainerProcessor->addContainerAccessor(
@@ -217,7 +223,7 @@ final class SymfonyExtension implements Extension
     /**
      * @param ExtensionManager $extensionManager
      */
-    private function initializeCrossContainerProcessor(ExtensionManager $extensionManager)
+    private function initializeCrossContainerProcessor(ExtensionManager $extensionManager): void
     {
         /** @var CrossContainerExtension $extension */
         $extension = $extensionManager->getExtension('fob_cross_container');
@@ -229,7 +235,7 @@ final class SymfonyExtension implements Extension
     /**
      * @param ExtensionManager $extensionManager
      */
-    private function registerSymfonyDriverFactory(ExtensionManager $extensionManager)
+    private function registerSymfonyDriverFactory(ExtensionManager $extensionManager): void
     {
         /** @var MinkExtension $minkExtension */
         $minkExtension = $extensionManager->getExtension('mink');
@@ -249,7 +255,7 @@ final class SymfonyExtension implements Extension
      *
      * @return string|null
      */
-    private function getKernelFile($basePath, $kernelPath)
+    private function getKernelFile(string $basePath, string $kernelPath): ?string
     {
         $possibleFiles = [
             sprintf('%s/%s', $basePath, $kernelPath),
@@ -271,7 +277,7 @@ final class SymfonyExtension implements Extension
      *
      * @throws \DomainException
      */
-    private function requireKernelBootstrapFile($basePath, $bootstrapPath)
+    private function requireKernelBootstrapFile(string $basePath, string $bootstrapPath): void
     {
         if (null === $bootstrapPath) {
             return;