diff --git a/src/Symfony/Component/DependencyInjection/CHANGELOG.md b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
index 9a41e8570551..25e7fc66aaaf 100644
--- a/src/Symfony/Component/DependencyInjection/CHANGELOG.md
+++ b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+2.5.0
+-----
+
+* added DecoratorServicePass and a way to override a service definition (Definition::setDecoratedService())
+
 2.4.0
 -----
 
diff --git a/src/Symfony/Component/DependencyInjection/Compiler/DecoratorServicePass.php b/src/Symfony/Component/DependencyInjection/Compiler/DecoratorServicePass.php
new file mode 100644
index 000000000000..c6db81148560
--- /dev/null
+++ b/src/Symfony/Component/DependencyInjection/Compiler/DecoratorServicePass.php
@@ -0,0 +1,54 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\DependencyInjection\Compiler;
+
+use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Alias;
+
+/**
+ * Overwrites a service but keeps the overridden one.
+ *
+ * @author Christophe Coevoet <stof@notk.org>
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+class DecoratorServicePass implements CompilerPassInterface
+{
+    public function process(ContainerBuilder $container)
+    {
+        foreach ($container->getDefinitions() as $id => $definition) {
+            if (!$decorated = $definition->getDecoratedService()) {
+                continue;
+            }
+
+            list ($decorated, $renamedId) = $decorated;
+            if (!$renamedId) {
+                $renamedId = $id.'.inner';
+            }
+
+            // we create a new alias/service for the service we are replacing
+            // to be able to reference it in the new one
+            if ($container->hasAlias($decorated)) {
+                $alias = $container->getAlias($decorated);
+                $public = $alias->isPublic();
+                $container->setAlias($renamedId, new Alias((string) $alias, false));
+            } else {
+                $definition = $container->getDefinition($decorated);
+                $public = $definition->isPublic();
+                $definition->setPublic(false);
+                $container->setDefinition($renamedId, $definition);
+            }
+
+            $container->setAlias($decorated, new Alias($id, $public));
+        }
+    }
+}
diff --git a/src/Symfony/Component/DependencyInjection/Compiler/PassConfig.php b/src/Symfony/Component/DependencyInjection/Compiler/PassConfig.php
index ac395db22e9a..bcef41052b9b 100644
--- a/src/Symfony/Component/DependencyInjection/Compiler/PassConfig.php
+++ b/src/Symfony/Component/DependencyInjection/Compiler/PassConfig.php
@@ -46,6 +46,7 @@ public function __construct()
 
         $this->optimizationPasses = array(
             new ResolveDefinitionTemplatesPass(),
+            new DecoratorServicePass(),
             new ResolveParameterPlaceHoldersPass(),
             new CheckDefinitionValidityPass(),
             new ResolveReferencesToAliasesPass(),
diff --git a/src/Symfony/Component/DependencyInjection/Definition.php b/src/Symfony/Component/DependencyInjection/Definition.php
index 428fee27c3a2..ce3646a9fb0b 100644
--- a/src/Symfony/Component/DependencyInjection/Definition.php
+++ b/src/Symfony/Component/DependencyInjection/Definition.php
@@ -38,6 +38,7 @@ class Definition
     private $abstract = false;
     private $synchronized = false;
     private $lazy = false;
+    private $decoratedService;
 
     protected $arguments;
 
@@ -100,6 +101,31 @@ public function setFactoryMethod($factoryMethod)
         return $this;
     }
 
+    /**
+     * Sets the service that this service is decorating.
+     *
+     * @param string $id        The decorated service id
+     * @param string $renamedId The new decorated service id
+     */
+    public function setDecoratedService($id, $renamedId = null)
+    {
+        if ($renamedId && $id == $renamedId) {
+            throw new \LogicException(sprintf('The decorated service parent name for "%s" must be different than the service name itself.', $id));
+        }
+
+        $this->decoratedService = array($id, $renamedId);
+    }
+
+    /**
+     * Gets the service that decorates this service.
+     *
+     * @return array An array composed of the decorated service id and the new id for it
+     */
+    public function getDecoratedService()
+    {
+        return $this->decoratedService;
+    }
+
     /**
      * Gets the factory method.
      *