diff --git a/lib/ace/mode/text_highlight_rules.js b/lib/ace/mode/text_highlight_rules.js
index b63f6c08..fc7bfb67 100644
--- a/lib/ace/mode/text_highlight_rules.js
+++ b/lib/ace/mode/text_highlight_rules.js
@@ -51,6 +51,11 @@ var TextHighlightRules = function() {
 (function() {
 
     this.addRules = function(rules, prefix) {
+        if (!prefix) {
+            for (var key in rules)
+                this.$rules[key] = rules[key];
+            return;
+        }
         for (var key in rules) {
             var state = rules[key];
             for (var i = 0; i < state.length; i++) {
@@ -96,7 +101,7 @@ var TextHighlightRules = function() {
         if (!this.$embeds)
             this.$embeds = [];
         this.$embeds.push(prefix);
-    }
+    };
 
     this.getEmbeds = function() {
         return this.$embeds;