diff --git a/src/extras/module-types.js b/src/extras/module-types.js
index 69daaa0b..ff8b628a 100644
--- a/src/extras/module-types.js
+++ b/src/extras/module-types.js
@@ -8,8 +8,9 @@ import { resolveUrl } from '../common.js';
   var systemJSPrototype = global.System.constructor.prototype;
 
   var moduleTypesRegEx = /^[^#?]+\.(css|html|json|wasm)([?#].*)?$/;
+  var _shouldFetch = systemJSPrototype.shouldFetch
   systemJSPrototype.shouldFetch = function (url) {
-    return moduleTypesRegEx.test(url);
+    return _shouldFetch(url) || moduleTypesRegEx.test(url);
   };
 
   var jsonContentType = /^application\/json(;|$)/;