diff --git a/bundles/org.eclipse.orion.client.editor/web/orion/editor/undoStack.js b/bundles/org.eclipse.orion.client.editor/web/orion/editor/undoStack.js
index <HASH>..<HASH> 100644
--- a/bundles/org.eclipse.orion.client.editor/web/orion/editor/undoStack.js
+++ b/bundles/org.eclipse.orion.client.editor/web/orion/editor/undoStack.js
@@ -266,7 +266,7 @@ define("orion/editor/undoStack", [], function() { //$NON-NLS-0$
 		 * @see orion.editor.UndoStack#markClean
 		 */
 		isClean: function() {
-			return this.cleanIndex === this.index && this._unsavedChanges.length === 0;
+			return this.cleanIndex === this.getSize().undo && this._unsavedChanges.length === 0;
 		},
 		/**
 		 * Returns true if there is at least one change to undo.
Bug <I> - File save operation should support sending file diffs