diff --git a/lib/marked.js b/lib/marked.js
index 8ab79819..e6f8804e 100644
--- a/lib/marked.js
+++ b/lib/marked.js
@@ -1144,8 +1144,13 @@ function merge(obj) {
  */
 
 function marked(src, opt, callback) {
-  // return null in case of non valid input
-  if (typeof src != 'string') return null;
+  // throw error in case of non string input
+  if (typeof src == 'undefined' || src === null)
+    throw new Error('marked(): input parameter is undefined or null');
+  if (typeof src != 'string')
+    throw new Error('marked(): input parameter is of type ' +
+      Object.prototype.toString.call(src) + ', string expected');
+
 
   if (callback || typeof opt === 'function') {
     if (!callback) {