diff --git a/IPython/frontend/html/notebook/static/js/completer.js b/IPython/frontend/html/notebook/static/js/completer.js
index a51c8b0..04e01b2 100644
--- a/IPython/frontend/html/notebook/static/js/completer.js
+++ b/IPython/frontend/html/notebook/static/js/completer.js
@@ -8,6 +8,13 @@ var IPython = (function (IPython) {
     // easyier key mapping
     var key = IPython.utils.keycodes;
 
+    function prepend_n_prc(str,n)
+    {
+        for( var i =0; i< n;i++)
+        { str = '%'+str }
+        return str;
+    }
+
     function _existing_completion(item, completion_array){
        for( var c in completion_array ) {
            if(completion_array[c].substr(-item.length) == item)
@@ -17,14 +24,26 @@ var IPython = (function (IPython) {
     }
 
     // what is the common start of all completions
-    function shared_start(B) {
+    function shared_start(B,drop_prct) {
         if (B.length == 1) {
             return B[0];
         }
         var A = new Array();
+        var common;
+        var min_lead_prct = 10;
         for (var i = 0; i < B.length; i++) {
-            A.push(B[i].str);
+            var str = B[i].str
+            var localmin = 0
+            if(drop_prct == true){
+                while ( str.substr(0,1) == '%') {
+                    localmin = localmin+1;
+                    str = str.substring(1);
+                }
+            }
+            min_lead_prct = Math.min(min_lead_prct,localmin);
+            A.push(str);
         }
+
         if (A.length > 1) {
             var tem1, tem2, s;
             A = A.slice(0).sort();
@@ -35,10 +54,10 @@ var IPython = (function (IPython) {
                 tem1 = tem1.substring(0, --s);
             }
             if (tem1 == "" || tem2.indexOf(tem1) != 0) {
-                return null;
+                return prepend_n_prc('',min_lead_prct);
             }
             return {
-                str: tem1,
+                str: prepend_n_prc(tem1,min_lead_prct),
                 type: "computed",
                 from: B[0].from,
                 to: B[0].to
@@ -257,7 +276,7 @@ var IPython = (function (IPython) {
             //Check that shared start is not null which can append with prefixed completion
             // like %pylab , pylab have no shred start, and ff will result in py<tab><tab>
             // to erase py
-            var sh = shared_start(this.raw_result);
+            var sh = shared_start(this.raw_result,true);
             if (sh) {
                 this.insert(sh);
             }