diff --git a/lib/ace/document.js b/lib/ace/document.js
index a5439bf8..9dd18674 100644
--- a/lib/ace/document.js
+++ b/lib/ace/document.js
@@ -592,6 +592,28 @@ var Document = function(text) {
         }
     };
 
+    this.indexToPosition = function(index, startRow) {
+        var lines = this.$lines || this.getAllLines();
+        var newlineLength = this.getNewLineCharacter().length;
+        for (var i = startRow || 0, l = lines.length; i < l; i++) {
+            index -= lines[i].length + newlineLength;
+            if (index < 0)
+                return {row: i, column: index + lines[i].length + newlineLength};
+        }
+        return {row: l-1, column: lines[l-1].length};
+    };
+
+    this.positionToIndex = function(pos, startRow) {
+        var lines = this.$lines || this.getAllLines();
+        var newlineLength = this.getNewLineCharacter().length;
+        var index = 0;
+        var row = Math.min(pos.row, lines.length);
+        for (var i = startRow || 0; i < row; ++i)
+            index += lines[i].length;
+
+        return index + newlineLength * i + pos.column;
+    };
+
 }).call(Document.prototype);
 
 exports.Document = Document;
diff --git a/lib/ace/mode/json_worker.js b/lib/ace/mode/json_worker.js
index bb72a7ac..9c233d77 100644
--- a/lib/ace/mode/json_worker.js
+++ b/lib/ace/mode/json_worker.js
@@ -50,7 +50,7 @@ oop.inherits(JsonWorker, Mirror);
         try {
             var result = parse(value);
         } catch (e) {
-            var pos = this.charToDocumentPosition(e.at-1);
+            var pos = this.doc.indexToPosition(e.at-1);
             this.sender.emit("error", {
                 row: pos.row,
                 column: pos.column,
@@ -62,35 +62,6 @@ oop.inherits(JsonWorker, Mirror);
         this.sender.emit("ok");
     };
 
-    this.charToDocumentPosition = function(charPos) {
-        var i = 0;
-        var len = this.doc.getLength();
-        var nl = this.doc.getNewLineCharacter().length;
-
-        if (!len) {
-            return { row: 0, column: 0};
-        }
-
-        var lineStart = 0;
-        while (i < len) {
-            var line = this.doc.getLine(i);
-            var lineLength = line.length + nl;
-            if (lineStart + lineLength > charPos)
-                return {
-                    row: i,
-                    column: charPos - lineStart
-                };
-
-            lineStart += lineLength;
-            i += 1;
-        }
-
-        return {
-            row: i-1,
-            column: line.length
-        };
-    };
-
 }).call(JsonWorker.prototype);
 
 });