diff --git a/lib/ace/undomanager.js b/lib/ace/undomanager.js
index 304dac23..4411ae8b 100644
--- a/lib/ace/undomanager.js
+++ b/lib/ace/undomanager.js
@@ -64,6 +64,7 @@ var UndoManager = function() {
         var deltas = options.args[0];
         this.$doc  = options.args[1];
         if (options.merge && this.hasUndo()){
+            this.dirtyCounter--;
             deltas = this.$undoStack.pop().concat(deltas);
         }
         this.$undoStack.push(deltas);