diff --git a/lib/ace/editor.js b/lib/ace/editor.js
index 7552a17a..6a68e5de 100644
--- a/lib/ace/editor.js
+++ b/lib/ace/editor.js
@@ -211,13 +211,14 @@ var Editor = function(renderer, session) {
         }
     };
 
+    // TODO use property on commands instead of this
+    this.$mergeableCommands = ["backspace", "del", "insertstring"];
     this.$historyTracker = function(e) {
         if (!this.$mergeUndoDeltas)
             return;
 
-
         var prev = this.prevOp;
-        var mergeableCommands = ["backspace", "del", "insertstring"];
+        var mergeableCommands = this.$mergeableCommands;
         // previous command was the same
         var shouldMerge = prev.command && (e.command.name == prev.command.name);
         if (e.command.name == "insertstring") {