diff --git a/lib/ace/placeholder.js b/lib/ace/placeholder.js
index f8141690..8092ca2e 100644
--- a/lib/ace/placeholder.js
+++ b/lib/ace/placeholder.js
@@ -60,7 +60,8 @@ var PlaceHolder = function(session, length, pos, others, mainClass, othersClass)
     
     this.$pos = pos;
     // Used for reset
-    this.$undoStackDepth = session.getUndoManager().$undostack ? session.getUndoManager().$undostack.length : -1;
+    var undoStack = session.getUndoManager().$undoStack || session.getUndoManager().$undostack || {length: -1};
+    this.$undoStackDepth =  undoStack.length;
     this.setup();
 
     session.selection.on("changeCursor", this.$onCursorChange);
@@ -202,7 +203,7 @@ var PlaceHolder = function(session, length, pos, others, mainClass, othersClass)
         if(this.$undoStackDepth === -1)
             throw Error("Canceling placeholders only supported with undo manager attached to session.");
         var undoManager = this.session.getUndoManager();
-        var undosRequired = undoManager.$undostack.length - this.$undoStackDepth;
+        var undosRequired = (undoManager.$undoStack || undoManager.$undostack).length - this.$undoStackDepth;
         for (var i = 0; i < undosRequired; i++) {
             undoManager.undo(true);
         }
diff --git a/lib/ace/placeholder_test.js b/lib/ace/placeholder_test.js
index bafb1de3..fb1ddf01 100644
--- a/lib/ace/placeholder_test.js
+++ b/lib/ace/placeholder_test.js
@@ -140,8 +140,6 @@ module.exports = {
     "test: cancel": function(next) {
         var session = new EditSession("var a = 10;\nconsole.log(a, a);", new JavaScriptMode());
         session.setUndoManager(new UndoManager());
-        // hack around the difference between full ACE context and C9 world
-        session.getUndoManager().$undostack = session.getUndoManager().$undoStack;
         var editor = new Editor(new MockRenderer(), session);
         var p = new PlaceHolder(session, 1, {row: 0, column: 4}, [{row: 1, column: 12}, {row: 1, column: 15}]);