diff --git a/src/helpers.js b/src/helpers.js
index 34b2750..9dce4e3 100644
--- a/src/helpers.js
+++ b/src/helpers.js
@@ -6,11 +6,15 @@ if (!showdown.hasOwnProperty('helper')) {
   showdown.helper = {};
 }
 
-if (typeof this.document === 'undefined' && typeof this.window === 'undefined') {
-  var jsdom = require('jsdom');
-  this.window = new jsdom.JSDOM('', {}).window; // jshint ignore:line
+if (typeof this === 'undefined' && typeof window !== 'undefined') {
+  showdown.helper.document = window.document;
+} else {
+  if (typeof this.document === 'undefined' && typeof this.window === 'undefined') {
+    var jsdom = require('jsdom');
+    this.window = new jsdom.JSDOM('', {}).window; // jshint ignore:line
+  }
+  showdown.helper.document = this.window.document;
 }
-showdown.helper.document = this.window.document;
 
 /**
  * Check if var is string