diff --git a/src/extras/module-types.js b/src/extras/module-types.js
index 69daaa0b..3f429aa6 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.bind(systemJSPrototype)
   systemJSPrototype.shouldFetch = function (url) {
-    return moduleTypesRegEx.test(url);
+    return _shouldFetch(url) || moduleTypesRegEx.test(url);
   };
 
   var jsonContentType = /^application\/json(;|$)/;
diff --git a/test/system-node.mjs b/test/system-node.mjs
index 3d505d37..2e3f881c 100644
--- a/test/system-node.mjs
+++ b/test/system-node.mjs
@@ -37,7 +37,7 @@ describe('NodeJS version of SystemJS', () => {
 
   describe('import maps', () => {
     it('can load a module from the network', async () => {
-      applyImportMap(System, {imports: {"rxjs": "https://unpkg.com/@esm-bundle/rxjs@6.5.4-fix.0/system/rxjs.min.js"}});
+      applyImportMap(System, {imports: {"rxjs": "https://cdn.jsdelivr.net/npm/@esm-bundle/rxjs@6.5.4-fix.0/system/rxjs.min.js"}});
       const rxjs = await System.import("rxjs");
       assert.ok(rxjs.Observable);
     });
@@ -48,4 +48,4 @@ describe('NodeJS version of SystemJS', () => {
       assert.equal(foo.p, 5);
     });
   });
-});
\ No newline at end of file
+});