diff --git a/UPGRADE-2.8.md b/UPGRADE-2.8.md
index 24861929c8ae5..6a7282172db12 100644
--- a/UPGRADE-2.8.md
+++ b/UPGRADE-2.8.md
@@ -21,7 +21,7 @@ Form
 
    ```php
    use Symfony\Component\Validator\Constraints\Valid;
-   
+
    $form = $this->createFormBuilder($article)
        ->add('author', new AuthorType(), array(
            'constraints' => new Valid(),
@@ -42,42 +42,42 @@ Form
        private $author;
    }
    ```
-   
+
  * Type names were deprecated and will be removed in Symfony 3.0. Instead of
    referencing types by name, you should reference them by their
    fully-qualified class name (FQCN) instead. With PHP 5.5 or later, you can
    use the "class" constant for that:
-   
+
    Before:
-   
+
    ```php
    $form = $this->createFormBuilder()
        ->add('name', 'text')
        ->add('age', 'integer')
        ->getForm();
    ```
-   
+
    After:
-   
+
    ```php
    use Symfony\Component\Form\Extension\Core\Type\IntegerType;
    use Symfony\Component\Form\Extension\Core\Type\TextType;
-   
+
    $form = $this->createFormBuilder()
        ->add('name', TextType::class)
        ->add('age', IntegerType::class)
        ->getForm();
    ```
-   
+
    As a further consequence, the method `FormTypeInterface::getName()` was
    deprecated and will be removed in Symfony 3.0. You should remove this method
    from your form types.
-   
+
    If you want to customize the block prefix of a type in Twig, you should now
    implement `FormTypeInterface::getBlockPrefix()` instead:
-   
+
    Before:
-   
+
    ```php
    class UserProfileType extends AbstractType
    {
@@ -87,9 +87,9 @@ Form
        }
    }
    ```
-   
+
    After:
-   
+
    ```php
    class UserProfileType extends AbstractType
    {
@@ -99,14 +99,14 @@ Form
        }
    }
    ```
-   
+
    If you don't customize `getBlockPrefix()`, it defaults to the class name
    without "Type" suffix in underscore notation (here: "user_profile").
-   
+
    If you want to create types that are compatible with Symfony 2.3 up to 2.8
    and don't trigger deprecation errors, implement *both* `getName()` and
    `getBlockPrefix()`:
-   
+
    ```php
    class ProfileType extends AbstractType
    {
@@ -114,38 +114,38 @@ Form
        {
            return $this->getBlockPrefix();
        }
-       
+
        public function getBlockPrefix()
        {
            return 'profile';
        }
    }
    ```
-   
+
    If you define your form types in the Dependency Injection configuration, you
    should further remove the "alias" attribute:
-   
+
    Before:
-   
+
    ```xml
    <service id="my.type" class="Vendor\Type\MyType">
        <tag name="form.type" alias="mytype" />
    </service>
    ```
-   
+
    After:
-   
+
    ```xml
    <service id="my.type" class="Vendor\Type\MyType">
        <tag name="form.type" />
    </service>
    ```
-   
+
    Type extension should return the fully-qualified class name of the extended
    type from `FormTypeExtensionInterface::getExtendedType()` now.
-   
+
    Before:
-   
+
    ```php
    class MyTypeExtension extends AbstractTypeExtension
    {
@@ -155,12 +155,12 @@ Form
        }
    }
    ```
-   
+
    After:
-   
+
    ```php
    use Symfony\Component\Form\Extension\Core\Type\FormType;
-   
+
    class MyTypeExtension extends AbstractTypeExtension
    {
        public function getExtendedType()
@@ -169,14 +169,14 @@ Form
        }
    }
    ```
-   
+
    If your extension has to be compatible with Symfony 2.3-2.8, use the 
    following statement:
-   
+
    ```php
    use Symfony\Component\Form\AbstractType;
    use Symfony\Component\Form\Extension\Core\Type\FormType;
-   
+
    class MyTypeExtension extends AbstractTypeExtension
    {
        public function getExtendedType()
@@ -185,13 +185,13 @@ Form
        }
    }
    ```
-   
+
  * Returning type instances from `FormTypeInterface::getParent()` is deprecated
    and will not be supported anymore in Symfony 3.0. Return the fully-qualified
    class name of the parent type class instead.
-   
+
    Before:
-   
+
    ```php
    class MyType
    {
@@ -201,9 +201,9 @@ Form
        }
    }
    ```
-   
+
    After:
-   
+
    ```php
    class MyType
    {
@@ -213,24 +213,28 @@ Form
        }
    }
    ```
-   
+
  * Passing type instances to `Form::add()`, `FormBuilder::add()` and the
    `FormFactory::create*()` methods is deprecated and will not be supported
    anymore in Symfony 3.0. Pass the fully-qualified class name of the type
    instead.
-   
+
    Before:
-   
+
    ```php
    $form = $this->createForm(new MyType());
    ```
-   
+
    After:
-   
+
    ```php
    $form = $this->createForm(MyType::class);
    ```
 
+ * Registering type extensions as a service with an alias which does not
+   match the type returned by `getExtendedType` is now forbidden. Fix your
+   implementation to define the right type.
+
 Translator
 ----------
 
diff --git a/src/Symfony/Component/Form/CHANGELOG.md b/src/Symfony/Component/Form/CHANGELOG.md
index 76b2da1da319d..cebd4b87ac473 100644
--- a/src/Symfony/Component/Form/CHANGELOG.md
+++ b/src/Symfony/Component/Form/CHANGELOG.md
@@ -9,6 +9,7 @@ CHANGELOG
  * deprecated the "cascade_validation" option in favor of setting "constraints"
    with the Valid constraint
  * moved data trimming logic of TrimListener into StringUtil
+ * [BC BREAK] When registering a type extension through the DI extension, the tag alias has to match the actual extended type.
 
 2.7.0
 -----
diff --git a/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php b/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php
index 487a9aa8b75ea..3a8a6b254523e 100644
--- a/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php
+++ b/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php
@@ -68,7 +68,18 @@ public function getTypeExtensions($name)
 
         if (isset($this->typeExtensionServiceIds[$name])) {
             foreach ($this->typeExtensionServiceIds[$name] as $serviceId) {
-                $extensions[] = $this->container->get($serviceId);
+                $extensions[] = $extension = $this->container->get($serviceId);
+
+                // validate result of getExtendedType() to ensure it is consistent with the service definition
+                if ($extension->getExtendedType() !== $name) {
+                    throw new InvalidArgumentException(
+                        sprintf('The extended type specified for the service "%s" does not match the actual extended type. Expected "%s", given "%s".',
+                            $serviceId,
+                            $name,
+                            $extension->getExtendedType()
+                        )
+                    );
+                }
             }
         }
 
diff --git a/src/Symfony/Component/Form/Tests/Extension/DependencyInjection/DependencyInjectionExtensionTest.php b/src/Symfony/Component/Form/Tests/Extension/DependencyInjection/DependencyInjectionExtensionTest.php
new file mode 100644
index 0000000000000..77fb370d73e0b
--- /dev/null
+++ b/src/Symfony/Component/Form/Tests/Extension/DependencyInjection/DependencyInjectionExtensionTest.php
@@ -0,0 +1,80 @@
+<?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\Form\Tests\Extension\DependencyInjection;
+
+use Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException;
+use Symfony\Component\Form\Extension\DependencyInjection\DependencyInjectionExtension;
+
+class DependencyInjectionExtensionTest extends \PHPUnit_Framework_TestCase
+{
+    public function testGetTypeExtensions()
+    {
+        $container = $this->getMock('Symfony\Component\DependencyInjection\ContainerInterface');
+
+        $typeExtension1 = $this->getMock('Symfony\Component\Form\FormTypeExtensionInterface');
+        $typeExtension1->expects($this->any())
+            ->method('getExtendedType')
+            ->willReturn('test');
+        $typeExtension2 = $this->getMock('Symfony\Component\Form\FormTypeExtensionInterface');
+        $typeExtension2->expects($this->any())
+            ->method('getExtendedType')
+            ->willReturn('test');
+        $typeExtension3 = $this->getMock('Symfony\Component\Form\FormTypeExtensionInterface');
+        $typeExtension3->expects($this->any())
+            ->method('getExtendedType')
+            ->willReturn('other');
+
+        $services = array(
+            'extension1' => $typeExtension1,
+            'extension2' => $typeExtension2,
+            'extension3' => $typeExtension3,
+        );
+
+        $container->expects($this->any())
+            ->method('get')
+            ->willReturnCallback(function ($id) use ($services) {
+                if (isset($services[$id])) {
+                    return $services[$id];
+                }
+
+                throw new ServiceNotFoundException($id);
+            });
+
+        $extension = new DependencyInjectionExtension($container, array(), array('test' => array('extension1', 'extension2'), 'other' => array('extension3')), array());
+
+        $this->assertTrue($extension->hasTypeExtensions('test'));
+        $this->assertFalse($extension->hasTypeExtensions('unknown'));
+        $this->assertSame(array($typeExtension1, $typeExtension2), $extension->getTypeExtensions('test'));
+    }
+
+    /**
+     * @expectedException \Symfony\Component\Form\Exception\InvalidArgumentException
+     */
+    public function testThrowExceptionForInvalidExtendedType()
+    {
+        $container = $this->getMock('Symfony\Component\DependencyInjection\ContainerInterface');
+
+        $typeExtension = $this->getMock('Symfony\Component\Form\FormTypeExtensionInterface');
+        $typeExtension->expects($this->any())
+            ->method('getExtendedType')
+            ->willReturn('unmatched');
+
+        $container->expects($this->any())
+            ->method('get')
+            ->with('extension')
+            ->willReturn($typeExtension);
+
+        $extension = new DependencyInjectionExtension($container, array(), array('test' => array('extension')), array());
+
+        $extension->getTypeExtensions('test');
+    }
+}
diff --git a/src/Symfony/Component/Form/composer.json b/src/Symfony/Component/Form/composer.json
index 66a8674ab70fd..b777792e1f327 100644
--- a/src/Symfony/Component/Form/composer.json
+++ b/src/Symfony/Component/Form/composer.json
@@ -26,6 +26,7 @@
         "symfony/phpunit-bridge": "~2.7|~3.0.0",
         "doctrine/collections": "~1.0",
         "symfony/validator": "~2.8|~3.0.0",
+        "symfony/dependency-injection": "~2.3|~3.0.0",
         "symfony/http-foundation": "~2.2|~3.0.0",
         "symfony/http-kernel": "~2.4|~3.0.0",
         "symfony/security-csrf": "~2.4|~3.0.0",

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