diff --git a/lib/ace/mode/jack.js b/lib/ace/mode/jack.js
index 327e200b..1ea02c24 100644
--- a/lib/ace/mode/jack.js
+++ b/lib/ace/mode/jack.js
@@ -49,6 +49,8 @@ oop.inherits(Mode, TextMode);
 
 (function() {
 
+    this.lineCommentStart = "--";
+
     this.getNextLineIndent = function(state, line, tab) {
         var indent = this.$getIndent(line);