diff --git a/lib/ace/document.js b/lib/ace/document.js
index 6f526227..ef2fab6d 100644
--- a/lib/ace/document.js
+++ b/lib/ace/document.js
@@ -691,7 +691,7 @@ var Document = function(text, mode) {
         return end;
     };
 
-    this.indentRows = function(startRow, endRow, indentString) {        
+    this.indentRows = function(startRow, endRow) {        
         indentString = indentString.replace("\t", this.getTabString());
         for (var row=startRow; row<=endRow; row++) {
             this.$insert({row: row, column:0}, indentString);