diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index 0ca30ea..1a4e0a0 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -29,6 +29,7 @@
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\RequestStack;
 use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpKernel\Exception\BadRequestHttpException;
 use Symfony\Component\HttpKernel\TerminableInterface;
 use Composer\Autoload\ClassLoader;
 
@@ -293,12 +294,28 @@ public function __construct($environment, $class_loader, $allow_dumping = TRUE)
    * @return string
    *   The path of the matching directory.
    *
+   * @throws BadRequestHttpException
+   *
    * @see \Drupal\Core\DrupalKernelInterface::getSitePath()
    * @see \Drupal\Core\DrupalKernelInterface::setSitePath()
    * @see default.settings.php
    * @see example.sites.php
    */
   public static function findSitePath(Request $request, $require_settings = TRUE) {
+    // Validate the hostname.  $request->getHost can also throw a
+    // UnexpectedValueException if it detects a bad hostname, but it does not
+    // validate the length.
+    // @todo Adjust per resolution to https://github.com/symfony/symfony/issues/12349
+    try {
+      $http_host = $request->getHost();
+      if (self::validateHostnameLength($http_host) == FALSE) {
+        throw new \UnexpectedValueException('Bad hostname');
+      }
+    }
+    catch (\UnexpectedValueException $e) {
+      throw new BadRequestHttpException('Bad hostname');
+    }
+
     // Check for a simpletest override.
     if ($test_prefix = drupal_valid_test_ua()) {
       return 'sites/simpletest/' . substr($test_prefix, 10);
@@ -315,9 +332,6 @@ public static function findSitePath(Request $request, $require_settings = TRUE)
       $script_name = $request->server->get('SCRIPT_FILENAME');
     }
     $http_host = $request->getHost();
-    if (self::validateHostnameLength($http_host) == FALSE) {
-      throw new \UnexpectedValueException('Bad hostname');
-    }
 
     $sites = array();
     include DRUPAL_ROOT . '/sites/sites.php';
diff --git a/index.php b/index.php
index 406d3dc..3de0a31 100644
--- a/index.php
+++ b/index.php
@@ -10,7 +10,9 @@
 
 use Drupal\Core\DrupalKernel;
 use Drupal\Core\Site\Settings;
+use Symfony\Component\HttpKernel\Exception\HttpException;
 use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
 
 $autoloader = require_once __DIR__ . '/core/vendor/autoload.php';
 
@@ -24,6 +26,11 @@
       ->prepare($request)->send();
   $kernel->terminate($request, $response);
 }
+catch (HttpException $e) {
+  $code = $e->getStatusCode();
+  http_response_code($code);
+  print Response::$statusTexts[$code];
+}
 catch (Exception $e) {
   $message = 'If you have just changed code (for example deployed a new module or moved an existing one) read <a href="http://drupal.org/documentation/rebuild">http://drupal.org/documentation/rebuild</a>';
   if (Settings::get('rebuild_access', FALSE)) {