diff --git a/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php b/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
index 6c9c1788f2..f73d223358 100644
--- a/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
+++ b/core/lib/Drupal/Core/Form/EventSubscriber/FormAjaxSubscriber.php
@@ -79,7 +79,8 @@ public function onException(GetResponseForExceptionEvent $event) {
       $response = new AjaxResponse();
       $status_messages = ['#type' => 'status_messages'];
       $response->addCommand(new PrependCommand(NULL, $status_messages));
-      $response->headers->set('X-Status-Code', 200);
+      $response->headers->set('Status-Code', 200);
+      $event->allowCustomResponseCode();
       $event->setResponse($response);
       return;
     }
@@ -99,7 +100,8 @@ public function onException(GetResponseForExceptionEvent $event) {
 
         // Since this response is being set in place of an exception, explicitly
         // mark this as a 200 status.
-        $response->headers->set('X-Status-Code', 200);
+        $response->headers->set('Status-Code', 200);
+        $event->allowCustomStatusCode();
         $event->setResponse($response);
       }
       catch (\Exception $e) {
diff --git a/core/tests/Drupal/Tests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php b/core/tests/Drupal/Tests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php
index 278ec06416..53b94486dd 100644
--- a/core/tests/Drupal/Tests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php
+++ b/core/tests/Drupal/Tests/Core/Form/EventSubscriber/FormAjaxSubscriberTest.php
@@ -76,7 +76,7 @@ public function testOnException() {
       ->willReturn($response);
 
     $event = $this->assertResponseFromException($request, $exception, $response);
-    $this->assertSame(200, $event->getResponse()->headers->get('X-Status-Code'));
+    $this->assertSame(200, $event->getResponse()->headers->get('Status-Code'));
   }
 
   /**
@@ -100,7 +100,7 @@ public function testOnExceptionNewBuildId() {
       ->willReturn($response);
 
     $event = $this->assertResponseFromException($request, $exception, $response);
-    $this->assertSame(200, $event->getResponse()->headers->get('X-Status-Code'));
+    $this->assertSame(200, $event->getResponse()->headers->get('Status-Code'));
   }
 
   /**
@@ -178,7 +178,7 @@ public function testOnExceptionBrokenPostRequest() {
     $this->subscriber->onException($event);
     $actual_response = $event->getResponse();
     $this->assertInstanceOf('\Drupal\Core\Ajax\AjaxResponse', $actual_response);
-    $this->assertSame(200, $actual_response->headers->get('X-Status-Code'));
+    $this->assertSame(200, $actual_response->headers->get('Status-Code'));
     $expected_commands[] = [
       'command' => 'insert',
       'method' => 'prepend',