diff --git a/core/lib/Drupal/Core/Ajax/AjaxResponse.php b/core/lib/Drupal/Core/Ajax/AjaxResponse.php
index 0ada14e..1bc3d7e 100644
--- a/core/lib/Drupal/Core/Ajax/AjaxResponse.php
+++ b/core/lib/Drupal/Core/Ajax/AjaxResponse.php
@@ -116,8 +116,30 @@ public function prepareResponse(Request $request) {
       $this->setData($this->ajaxRender($request));
     }
 
-    // Add proper HTTP Header for IE.
+    // IE 9 does not support XHR 2 (http://caniuse.com/#feat=xhr2), so
+    // for that browser, jquery.form submits requests containing a file upload
+    // via an IFRAME rather than via XHR. Since the response is being sent to
+    // an IFRAME, it must be formatted as HTML. Specifically:
+    // - It must use the text/html content type or else the browser will
+    //   present a download prompt. Note: This applies to both file uploads
+    //   as well as any ajax request in a form with a file upload form.
+    // - It must place the JSON data into a textarea to prevent browser
+    //   extensions such as Linkification and Skype's Browser Highlighter
+    //   from applying HTML transformations such as URL or phone number to
+    //   link conversions on the data values.
+    //
+    // Since this affects the format of the output, it could be argued that
+    // this should be implemented as a separate Accept MIME type. However,
+    // that would require separate variants for each type of AJAX request
+    // (e.g., drupal-ajax, drupal-dialog, drupal-modal), so for expediency,
+    // this browser workaround is implemented via a GET or POST parameter.
+    //
+    // @see http://malsup.com/jquery/form/#file-upload
+    // @see https://drupal.org/node/1009382
+    // @see https://drupal.org/node/2339491
+    // @see Drupal.ajax.prototype.beforeSend()
     $accept = $request->headers->get('accept');
+
     if (strpos($accept, 'text/html') !== FALSE) {
       $this->headers->set('Content-Type', 'text/html; charset=utf-8');
 
diff --git a/core/tests/Drupal/Tests/Core/Ajax/AjaxResponseTest.php b/core/tests/Drupal/Tests/Core/Ajax/AjaxResponseTest.php
index 0ddb9a4..19bbe8d 100644
--- a/core/tests/Drupal/Tests/Core/Ajax/AjaxResponseTest.php
+++ b/core/tests/Drupal/Tests/Core/Ajax/AjaxResponseTest.php
@@ -8,7 +8,9 @@
 namespace Drupal\Tests\Core\Ajax;
 
 use Drupal\Core\Ajax\AjaxResponse;
+use Drupal\Core\Render\Element\Ajax;
 use Drupal\Tests\UnitTestCase;
+use Symfony\Component\HttpFoundation\Request;
 
 /**
  * @coversDefaultClass \Drupal\Core\Ajax\AjaxResponse
@@ -68,5 +70,21 @@ public function testCommands() {
     $this->assertSame($commands[0], array('command' => 'three', 'class' => 'test-class'));
   }
 
+  /**
+   * Tests the support for IE specific headers in file uploads.
+   *
+   * @cover ::prepareResponse
+   */
+  public function testPrepareResponseForIeFormRequestsWithFileUpload() {
+    $request = Request::create('/example', 'POST');
+    $request->headers->set('Accept', 'text/html');
+    $response = new AjaxResponse([]);
+    $response->headers->set('Content-Type', 'application/json; charset=utf-8');
+
+    $response->prepare($request);
+    $this->assertEquals('text/html; charset=utf-8', $response->headers->get('Content-Type'));
+    $this->assertEquals($response->getContent(), '<textarea>[]</textarea>');
+  }
+
 
 }