diff --git a/UPGRADE-4.0.md b/UPGRADE-4.0.md
index fba86ef01c..3aecb70070 100644
--- a/UPGRADE-4.0.md
+++ b/UPGRADE-4.0.md
@@ -184,6 +184,8 @@ DependencyInjection
 
  * Top-level anonymous services in XML are no longer supported.
 
+ * The `ExtensionCompilerPass` has been moved to before-optimization passes with priority -1000.
+
 EventDispatcher
 ---------------
 
diff --git a/src/Symfony/Component/DependencyInjection/CHANGELOG.md b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
index bc8fd30518..cea65b20b7 100644
--- a/src/Symfony/Component/DependencyInjection/CHANGELOG.md
+++ b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
@@ -4,6 +4,7 @@ CHANGELOG
 3.4.0
 -----
 
+ * moved the `ExtensionCompilerPass` to before-optimization passes with priority -1000
  * deprecated "public-by-default" definitions and aliases, the new default will be "private" in 4.0
  * added `EnvVarProcessorInterface` and corresponding "container.env_var_processor" tag for processing env vars
  * added support for ignore-on-uninitialized references
diff --git a/src/Symfony/Component/DependencyInjection/Compiler/PassConfig.php b/src/Symfony/Component/DependencyInjection/Compiler/PassConfig.php
index 9e00be6827..79792bee4a 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/PassConfig.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/PassConfig.php
@@ -45,10 +45,10 @@ class PassConfig
                 new ResolveInstanceofConditionalsPass(),
                 new RegisterEnvVarProcessorsPass(),
             ),
+            -1000 => array(new ExtensionCompilerPass()),
         );
 
         $this->optimizationPasses = array(array(
-            new ExtensionCompilerPass(),
             new ResolveChildDefinitionsPass(),
             new ServiceLocatorTagPass(),
             new DecoratorServicePass(),
diff --git a/src/Symfony/Component/HttpKernel/CHANGELOG.md b/src/Symfony/Component/HttpKernel/CHANGELOG.md
index 702394ade5..8732b17dd8 100644
--- a/src/Symfony/Component/HttpKernel/CHANGELOG.md
+++ b/src/Symfony/Component/HttpKernel/CHANGELOG.md
@@ -4,6 +4,7 @@ CHANGELOG
 3.4.0
 -----
 
+ * made kernels implementing `CompilerPassInterface` able to process the container
  * deprecated bundle inheritance
  * added `RebootableInterface` and implemented it in `Kernel`
  * deprecated commands auto registration
diff --git a/src/Symfony/Component/HttpKernel/Kernel.php b/src/Symfony/Component/HttpKernel/Kernel.php
index 4f7ec2c289..cd4c26063d 100644
--- a/src/Symfony/Component/HttpKernel/Kernel.php
+++ b/src/Symfony/Component/HttpKernel/Kernel.php
@@ -13,6 +13,8 @@ namespace Symfony\Component\HttpKernel;
 
 use Symfony\Bridge\ProxyManager\LazyProxy\Instantiator\RuntimeInstantiator;
 use Symfony\Bridge\ProxyManager\LazyProxy\PhpDumper\ProxyDumper;
+use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
+use Symfony\Component\DependencyInjection\Compiler\PassConfig;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Dumper\PhpDumper;
@@ -767,6 +769,9 @@ abstract class Kernel implements KernelInterface, RebootableInterface, Terminabl
         $container = new ContainerBuilder();
         $container->getParameterBag()->add($this->getKernelParameters());
 
+        if ($this instanceof CompilerPassInterface) {
+            $container->addCompilerPass($this, PassConfig::TYPE_BEFORE_OPTIMIZATION, -10000);
+        }
         if (class_exists('ProxyManager\Configuration') && class_exists('Symfony\Bridge\ProxyManager\LazyProxy\Instantiator\RuntimeInstantiator')) {
             $container->setProxyInstantiator(new RuntimeInstantiator());
         }
diff --git a/src/Symfony/Component/HttpKernel/Tests/KernelTest.php b/src/Symfony/Component/HttpKernel/Tests/KernelTest.php
index a408f87f87..fd7f6f09da 100644
--- a/src/Symfony/Component/HttpKernel/Tests/KernelTest.php
+++ b/src/Symfony/Component/HttpKernel/Tests/KernelTest.php
@@ -13,6 +13,7 @@ namespace Symfony\Component\HttpKernel\Tests;
 
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Config\Loader\LoaderInterface;
+use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\Filesystem\Filesystem;
 use Symfony\Component\HttpKernel\Bundle\BundleInterface;
@@ -831,6 +832,14 @@ EOF;
         $this->assertFileNotExists($containerFile);
     }
 
+    public function testKernelPass()
+    {
+        $kernel = new PassKernel();
+        $kernel->boot();
+
+        $this->assertTrue($kernel->getContainer()->getParameter('test.processed'));
+    }
+
     /**
      * Returns a mock for the BundleInterface.
      *
@@ -967,3 +976,17 @@ class CustomProjectDirKernel extends Kernel
         }
     }
 }
+
+class PassKernel extends CustomProjectDirKernel implements CompilerPassInterface
+{
+    public function __construct(\Closure $buildContainer = null)
+    {
+        parent::__construct();
+        Kernel::__construct('pass', true);
+    }
+
+    public function process(ContainerBuilder $container)
+    {
+        $container->setParameter('test.processed', true);
+    }
+}