diff --git a/lib/marked.js b/lib/marked.js
index 11b2e110f1..c607ca2ce1 100644
--- a/lib/marked.js
+++ b/lib/marked.js
@@ -1083,37 +1083,75 @@ function marked(src, opt, callback) {
       callback = opt;
       opt = null;
     }
+
     opt = merge({}, marked.defaults, opt || {});
-  }
-  try {
-    var renderer = null;
-    if (opt) {
-      opt = merge({}, marked.defaults, opt);
-      renderer = opt.renderer || null;
+
+    var highlight = opt.highlight
+      , tokens
+      , pending
+      , i = 0;
+
+    try {
+      tokens = Lexer.lex(src, opt)
+    } catch (e) {
+      return callback(e);
     }
-    var out = Parser.parse(Lexer.lex(src, opt), opt, renderer);
-    if (callback) {
-      return callback(null, out);
-    } else {
-      return out;
+
+    pending = tokens.length;
+
+    var done = function() {
+      var out, err;
+
+      try {
+        out = Parser.parse(tokens, opt, opt.renderer);
+      } catch (e) {
+        err = e;
+      }
+
+      opt.highlight = highlight;
+
+      return err
+        ? callback(err)
+        : callback(null, out);
+    };
+
+    if (!highlight || highlight.length < 3) {
+      return done();
     }
+
+    delete opt.highlight;
+
+    if (!pending) return done();
+
+    for (; i < tokens.length; i++) {
+      (function(token) {
+        if (token.type !== 'code') {
+          return --pending || done();
+        }
+        return highlight(token.text, token.lang, function(err, code) {
+          if (code == null || code === token.text) {
+            return --pending || done();
+          }
+          token.text = code;
+          token.escaped = true;
+          --pending || done();
+        });
+      })(tokens[i]);
+    }
+
+    return;
+  }
+  try {
+    if (opt) opt = merge({}, marked.defaults, opt);
+    return Parser.parse(Lexer.lex(src, opt), opt, opt && opt.renderer);
   } catch (e) {
     e.message += '\nPlease report this to https://github.com/chjj/marked.';
     if ((opt || marked.defaults).silent) {
-      var msg = '<p>An error occured:</p><pre>'
+      return '<p>An error occured:</p><pre>'
         + escape(e.message + '', true)
         + '</pre>';
-      if (callback) {
-        callback(msg);
-      } else {
-        return msg;
-      }
-    }
-    if (callback) {
-      callback(e);
-    } else {
-      throw e;
     }
+    throw e;
   }
 }
 
@@ -1159,13 +1197,13 @@ marked.inlineLexer = InlineLexer.output;
 marked.parse = marked;
 
 if (typeof exports === 'object') {
-    module.exports = marked;
+  module.exports = marked;
 } else if (typeof define === 'function' && define.amd) {
-    define(function() { return marked; });
+  define(function() { return marked; });
 } else {
-    this.marked = marked;
+  this.marked = marked;
 }
 
 }).call(function() {
-    return this || (typeof window !== 'undefined' ? window : global);
+  return this || (typeof window !== 'undefined' ? window : global);
 }());