diff --git a/demo/browser-polyfills.js b/demo/browser-polyfills.js
new file mode 100644
index 00000000..d62d41a6
--- /dev/null
+++ b/demo/browser-polyfills.js
@@ -0,0 +1,26 @@
+"use strict";
+
+// Polyfills for browsers that do not support String.trimLeft/Right
+function trimLeftPolyfill() {
+  return this.replace(/^\s*/, "");
+}
+/* istanbul ignore if */
+if (!String.prototype.trimLeft) {
+  String.prototype.trimLeft = trimLeftPolyfill;
+}
+function trimRightPolyfill() {
+  return this.replace(/\s*$/, "");
+}
+/* istanbul ignore if */
+if (!String.prototype.trimRight) {
+  String.prototype.trimRight = trimRightPolyfill;
+}
+
+// Export for testing
+/* istanbul ignore else */
+if ((typeof module !== "undefined") && module.exports) {
+  module.exports = {
+    "trimLeftPolyfill": trimLeftPolyfill,
+    "trimRightPolyfill": trimRightPolyfill
+  };
+}
diff --git a/demo/default.htm b/demo/default.htm
index 3f7b532a..e7cb66bb 100644
--- a/demo/default.htm
+++ b/demo/default.htm
@@ -27,6 +27,7 @@
       <footer>Copyright &copy; 2015 by <a href="//dlaa.me/">David Anson</a></footer>
     </div>
   </div>
+  <script src="browser-polyfills.js"></script>
   <script src="../node_modules/markdown-it/dist/markdown-it.min.js"></script>
   <script src="require-stub.js"></script>
   <script src="markdownlint-browser.js"></script>
diff --git a/package.json b/package.json
index bd78d54c..e2dce25c 100644
--- a/package.json
+++ b/package.json
@@ -15,7 +15,7 @@
     "test": "nodeunit",
     "test-cover": "istanbul cover node_modules/nodeunit/bin/nodeunit",
     "debug": "node debug node_modules/nodeunit/bin/nodeunit",
-    "lint": "eslint lib test & eslint --env browser --global markdownit --global markdownlint --rule \"no-unused-vars: 0\" demo & eslint --rule \"no-console: 0, no-shadow: 0\" example",
+    "lint": "eslint lib test & eslint --env browser --global markdownit --global markdownlint --rule \"no-unused-vars: 0, no-extend-native: 0\" demo & eslint --rule \"no-console: 0, no-shadow: 0\" example",
     "build-demo": "browserify lib/markdownlint.js --standalone markdownlint --exclude markdown-it --outfile demo/markdownlint-browser.js",
     "example": "npm install through2 & cd example & node standalone.js & grunt markdownlint & gulp markdownlint"
   },
diff --git a/test/markdownlint-test.js b/test/markdownlint-test.js
index 897cbc12..74b03bc5 100644
--- a/test/markdownlint-test.js
+++ b/test/markdownlint-test.js
@@ -7,6 +7,7 @@ var Q = require("q");
 var markdownlint = require("../lib/markdownlint");
 var shared = require("../lib/shared");
 var rules = require("../lib/rules");
+var polyfills = require("../demo/browser-polyfills");
 
 function createTestForFile(file) {
   return function testForFile(test) {
@@ -667,3 +668,31 @@ module.exports.typeAllFiles = function typeAllFiles(test) {
   });
   test.done();
 };
+
+module.exports.trimPolyfills = function trimPolyfills(test) {
+  var inputs = [
+    "text text",
+    " text text ",
+    "   text text   ",
+    // ECMAScript Whitespace
+    "\u0009 text text \u0009",
+    "\u000b text text \u000b",
+    "\u000c text text \u000c",
+    "\u0020 text text \u0020",
+    "\u00a0 text text \u00a0",
+    "\ufeff text text \ufeff",
+    // ECMAScript LineTerminator
+    "\u000a text text \u000a",
+    "\u000d text text \u000d",
+    "\u2028 text text \u2028",
+    "\u2029 text text \u2029"
+  ];
+  test.expect(inputs.length * 2);
+  inputs.forEach(function forInput(input) {
+    test.equal(polyfills.trimLeftPolyfill.call(input), input.trimLeft(),
+      "trimLeft incorrect for '" + input + "'");
+    test.equal(polyfills.trimRightPolyfill.call(input), input.trimRight(),
+      "trimRight incorrect for '" + input + "'");
+  });
+  test.done();
+};