diff --git a/lib/ace/undomanager.js b/lib/ace/undomanager.js
index 304dac23..4d978d46 100644
--- a/lib/ace/undomanager.js
+++ b/lib/ace/undomanager.js
@@ -61,14 +61,19 @@ var UndoManager = function() {
      *
      **/
     this.execute = function(options) {
-        var deltas = options.args[0];
+        
+        // Normalize deltas for storage.
+        var deltaSets = this.$serializeDeltas(options.args[0]);
+        
+        // Add deltas to undo stack.
         this.$doc  = options.args[1];
         if (options.merge && this.hasUndo()){
-            deltas = this.$undoStack.pop().concat(deltas);
+            deltaSets = this.$undoStack.pop().concat(deltaSets);
         }
-        this.$undoStack.push(deltas);
+        this.$undoStack.push(deltaSets);
+        
+        // Reset redo stack.
         this.$redoStack = [];
-
         if (this.dirtyCounter < 0) {
             // The user has made a change after undoing past the last clean state.
             // We can never get back to a clean state now until markClean() is called.
@@ -85,12 +90,11 @@ var UndoManager = function() {
      * @returns {Range} The range of the undo.
      **/
     this.undo = function(dontSelect) {
-        var deltas = this.$undoStack.pop();
+        var deltaSets = this.$undoStack.pop();
         var undoSelectionRange = null;
-        if (deltas) {
-            undoSelectionRange =
-                this.$doc.undoChanges(deltas, dontSelect);
-            this.$redoStack.push(deltas);
+        if (deltaSets) {
+            undoSelectionRange = this.$doc.undoChanges(this.$deserializeDeltas(deltaSets), dontSelect);
+            this.$redoStack.push(deltaSets);
             this.dirtyCounter--;
         }
 
@@ -104,15 +108,14 @@ var UndoManager = function() {
      * 
      **/
     this.redo = function(dontSelect) {
-        var deltas = this.$redoStack.pop();
+        var deltaSets = this.$redoStack.pop();
         var redoSelectionRange = null;
-        if (deltas) {
+        if (deltaSets) {
             redoSelectionRange =
-                this.$doc.redoChanges(deltas, dontSelect);
-            this.$undoStack.push(deltas);
+                this.$doc.redoChanges(this.$deserializeDeltas(deltaSets), dontSelect);
+            this.$undoStack.push(deltaSets);
             this.dirtyCounter++;
         }
-
         return redoSelectionRange;
     };
 
@@ -160,7 +163,54 @@ var UndoManager = function() {
     this.isClean = function() {
         return this.dirtyCounter === 0;
     };
-
+    
+    // Serializes deltaSets to reduce memory usage.
+    this.$serializeDeltas = function(deltaSets)
+    {
+        return this.$cloneDeltaSetsObj(deltaSets, $serializeDelta);
+    }
+    function $serializeDelta(delta){
+        return {
+            action: delta.action,
+            range:  delta.range,
+            lines: (delta.lines.length == 1 ? null           : delta.lines),
+            text:  (delta.lines.length == 1 ? delta.lines[0] : null       ),
+        };
+    }
+    
+    // Deserializes deltaSets to allow application to the document.
+    this.$deserializeDeltas = function(deltaSets)
+    {
+        return this.$cloneDeltaSetsObj(deltaSets, $deserializeDelta);
+    }
+    function $deserializeDelta(delta){
+        return {
+            action: delta.action,
+            range:  delta.range,
+            lines: (delta.text === null ? delta.lines : [delta.text])
+        };
+    }
+    
+    // Helper for delta serialization and deserialization.
+    this.$cloneDeltaSetsObj = function(deltaSets_old, fnGetModifiedDelta)
+    {
+        var deltaSets_new = new Array(deltaSets_old.length);
+        for (var i in deltaSets_old)
+        {
+            var deltaSet_old = deltaSets_old[i];
+            var deltaSet_new = { group: deltaSet_old.group, deltas: new Array(deltaSet_old.length)};
+            
+            for (var i_ in deltaSet_old.deltas)
+            {
+                var delta_old = deltaSet_old.deltas[i_];
+                deltaSet_new.deltas[i_] = fnGetModifiedDelta(delta_old);
+            }
+            
+            deltaSets_new[i] = deltaSet_new;
+        }
+        return deltaSets_new;        
+    }
+    
 }).call(UndoManager.prototype);
 
 exports.UndoManager = UndoManager;