diff --git a/src/Symfony/Component/Form/Extension/Core/Type/FileType.php b/src/Symfony/Component/Form/Extension/Core/Type/FileType.php
index f8afce2ee5..bb1c448098 100644
--- a/src/Symfony/Component/Form/Extension/Core/Type/FileType.php
+++ b/src/Symfony/Component/Form/Extension/Core/Type/FileType.php
@@ -20,7 +20,8 @@ use Symfony\Component\Form\FormInterface;
 use Symfony\Component\Form\FormView;
 use Symfony\Component\OptionsResolver\Options;
 use Symfony\Component\OptionsResolver\OptionsResolver;
-use Symfony\Component\Translation\TranslatorInterface;
+use Symfony\Component\Translation\TranslatorInterface as LegacyTranslatorInterface;
+use Symfony\Contracts\Translation\TranslatorInterface;
 
 class FileType extends AbstractType
 {
@@ -35,8 +36,14 @@ class FileType extends AbstractType
 
     private $translator;
 
-    public function __construct(TranslatorInterface $translator = null)
+    /**
+     * @param TranslatorInterface|null $translator
+     */
+    public function __construct($translator = null)
     {
+        if (null !== $translator && !$translator instanceof LegacyTranslatorInterface && !$translator instanceof TranslatorInterface) {
+            throw new \TypeError(sprintf('Argument 1 passed to %s() must be an instance of %s, %s given.', __METHOD__, TranslatorInterface::class, \is_object($translator) ? \get_class($translator) : \gettype($translator)));
+        }
         $this->translator = $translator;
     }
 
diff --git a/src/Symfony/Component/Form/Tests/Extension/Core/Type/FileTypeTest.php b/src/Symfony/Component/Form/Tests/Extension/Core/Type/FileTypeTest.php
index 311529c294..0731942c89 100644
--- a/src/Symfony/Component/Form/Tests/Extension/Core/Type/FileTypeTest.php
+++ b/src/Symfony/Component/Form/Tests/Extension/Core/Type/FileTypeTest.php
@@ -17,7 +17,7 @@ use Symfony\Component\Form\NativeRequestHandler;
 use Symfony\Component\Form\RequestHandlerInterface;
 use Symfony\Component\HttpFoundation\File\File;
 use Symfony\Component\HttpFoundation\File\UploadedFile;
-use Symfony\Component\Translation\TranslatorInterface;
+use Symfony\Contracts\Translation\TranslatorInterface;
 
 class FileTypeTest extends BaseTypeTest
 {
diff --git a/src/Symfony/Component/Serializer/Normalizer/DataUriNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/DataUriNormalizer.php
index 3ab7bd45f8..111f3f2ff4 100644
--- a/src/Symfony/Component/Serializer/Normalizer/DataUriNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/DataUriNormalizer.php
@@ -34,7 +34,7 @@ class DataUriNormalizer implements NormalizerInterface, DenormalizerInterface, C
     ];
 
     /**
-     * @var MimeTypeGuesserInterface
+     * @var MimeTypeGuesserInterface|null
      */
     private $mimeTypeGuesser;
 
diff --git a/src/Symfony/Component/Serializer/composer.json b/src/Symfony/Component/Serializer/composer.json
index 09c38137cd..087289fd7f 100644
--- a/src/Symfony/Component/Serializer/composer.json
+++ b/src/Symfony/Component/Serializer/composer.json
@@ -45,7 +45,7 @@
         "symfony/yaml": "For using the default YAML mapping loader.",
         "symfony/config": "For using the XML mapping loader.",
         "symfony/property-access": "For using the ObjectNormalizer.",
-        "symfony/http-foundation": "To use the DataUriNormalizer.",
+        "symfony/http-foundation": "For using a MIME type guesser within the DataUriNormalizer.",
         "doctrine/annotations": "For using the annotation mapping. You will also need doctrine/cache.",
         "doctrine/cache": "For using the default cached annotation reader and metadata cache."
     },