diff --git a/lib/outputrenderers.php b/lib/outputrenderers.php
index da3dbc73be9..9625b93e784 100644
--- a/lib/outputrenderers.php
+++ b/lib/outputrenderers.php
@@ -3344,9 +3344,19 @@ class core_renderer_ajax extends core_renderer {
      * Prepares the start of an AJAX output.
      */
     public function header() {
+        // MDL-39810: IE doesn't support JSON MIME type if version < 8 or when it runs in Compatibility View.
+        $supports_json_contenttype = !check_browser_version('MSIE') ||
+                (check_browser_version('MSIE', 8) &&
+                    !(preg_match("/MSIE 7.0/", $_SERVER['HTTP_USER_AGENT']) && preg_match("/Trident\/([0-9\.]+)/", $_SERVER['HTTP_USER_AGENT'])));
         // unfortunately YUI iframe upload does not support application/json
         if (!empty($_FILES)) {
             @header('Content-type: text/plain; charset=utf-8');
+            if (!$supports_json_contenttype) {
+                @header('X-Content-Type-Options: nosniff');
+            }
+        } else if (!$supports_json_contenttype) {
+            @header('Content-type: text/plain; charset=utf-8');
+            @header('X-Content-Type-Options: nosniff');
         } else {
             @header('Content-type: application/json; charset=utf-8');
         }