diff --git a/lib/ace/undomanager.js b/lib/ace/undomanager.js
index 4f7626fe..599e9158 100644
--- a/lib/ace/undomanager.js
+++ b/lib/ace/undomanager.js
@@ -65,6 +65,13 @@ var UndoManager = function() {
         this.$doc  = options.args[1];
         this.$undoStack.push(deltas);
         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.
+            this.dirtyCounter = NaN;
+        }
+        this.dirtyCounter++;
     };
 
     /**
@@ -82,6 +89,8 @@ var UndoManager = function() {
                 this.$doc.undoChanges(deltas, dontSelect);
             this.$redoStack.push(deltas);
         }
+
+        this.dirtyCounter--;
         return undoSelectionRange;
     };
 
@@ -99,6 +108,8 @@ var UndoManager = function() {
                 this.$doc.redoChanges(deltas, dontSelect);
             this.$undoStack.push(deltas);
         }
+
+        this.dirtyCounter++;
         return redoSelectionRange;
     };
 
@@ -109,6 +120,7 @@ var UndoManager = function() {
     this.reset = function() {
         this.$undoStack = [];
         this.$redoStack = [];
+        this.dirtyCounter = 0;
     };
 
     /**
@@ -129,6 +141,23 @@ var UndoManager = function() {
         return this.$redoStack.length > 0;
     };
 
+    /**
+    *
+    * Marks the current status clean
+    **/
+    this.markClean = function() {
+        this.dirtyCounter = 0;
+    };
+
+    /**
+    *
+    * Returns if the current status is clean
+    * @returns {Boolean}
+    **/
+    this.isClean = function() {
+        return this.dirtyCounter === 0;
+    };
+
 }).call(UndoManager.prototype);
 
 exports.UndoManager = UndoManager;