diff --git a/core/lib/Drupal/Core/File/MimeType/MimeTypeGuesser.php b/core/lib/Drupal/Core/File/MimeType/MimeTypeGuesser.php
index cac7a66158988446062f1819fd1babf8438bdd79..ae750502c4bd65bf373a3ce92ac8f41ee9bcb659 100644
--- a/core/lib/Drupal/Core/File/MimeType/MimeTypeGuesser.php
+++ b/core/lib/Drupal/Core/File/MimeType/MimeTypeGuesser.php
@@ -118,21 +118,9 @@ protected function sortGuessers() {
    * @see \Symfony\Component\HttpFoundation\File\MimeType\MimeTypeGuesser
    */
   public static function registerWithSymfonyGuesser(ContainerInterface $container) {
+    // Reset state, so we do not store more and more services during test runs.
+    SymfonyMimeTypeGuesser::reset();
     $singleton = SymfonyMimeTypeGuesser::getInstance();
-
-    // @todo Remove once Symfony adds a reset() method.
-    $property = new \ReflectionProperty(get_class($singleton), 'guessers');
-    $property->setAccessible(TRUE);
-
-    if (isset($singleton->_beforeDrupalRegistration)) {
-      // Reset state, else we store more and more services during test runs.
-      $property->setValue($singleton, $singleton->_beforeDrupalRegistration);
-    } else {
-      // Store original state before we register our services.
-      $singleton->_beforeDrupalRegistration = $property->getValue($singleton);
-    }
-
-    //$singleton->reset();
     $singleton->register($container->get('file.mime_type.guesser'));
   }
 
diff --git a/core/tests/Drupal/Tests/Core/File/MimeTypeGuesserTest.php b/core/tests/Drupal/Tests/Core/File/MimeTypeGuesserTest.php
index 9a712a637510e3b3a51911596ed06bd3bf5a5ad1..6e3f0e830fc604fd6509bd4edd36da8b22db844b 100644
--- a/core/tests/Drupal/Tests/Core/File/MimeTypeGuesserTest.php
+++ b/core/tests/Drupal/Tests/Core/File/MimeTypeGuesserTest.php
@@ -37,14 +37,18 @@ public function testSymfonyGuesserRegistration() {
     $container = new ContainerBuilder();
     $container->set('file.mime_type.guesser', new MimeTypeGuesser(new StreamWrapperManager()));
     MimeTypeGuesser::registerWithSymfonyGuesser($container);
+    $symfony_guesser = SymfonyMimeTypeGuesser::getInstance();
     $guessers = $this->readAttribute($symfony_guesser, 'guessers');
+    $this->assertSame($container->get('file.mime_type.guesser'), $guessers[0]);
     $this->assertInstanceOf('Drupal\Core\File\MimeType\MimeTypeGuesser', $guessers[0]);
     $count = count($guessers);
 
     $container = new ContainerBuilder();
     $container->set('file.mime_type.guesser', new MimeTypeGuesser(new StreamWrapperManager()));
     MimeTypeGuesser::registerWithSymfonyGuesser($container);
+    $symfony_guesser = SymfonyMimeTypeGuesser::getInstance();
     $guessers = $this->readAttribute($symfony_guesser, 'guessers');
+    $this->assertSame($container->get('file.mime_type.guesser'), $guessers[0]);
     $this->assertInstanceOf('Drupal\Core\File\MimeType\MimeTypeGuesser', $guessers[0]);
     $new_count = count($guessers);
     $this->assertEquals($count, $new_count, 'The count of mime type guessers remains the same after container re-init.');