diff --git a/src/app/text-mate-grammar.coffee b/src/app/text-mate-grammar.coffee
index d78446461..5978b99ce 100644
--- a/src/app/text-mate-grammar.coffee
+++ b/src/app/text-mate-grammar.coffee
@@ -26,6 +26,7 @@ class TextMateGrammar
       @repository[name] = new Rule(this, data)
 
   getLineTokens: (line, stack=[@initialRule]) ->
+    stack = new Array(stack...) # clone stack
     tokens = []
     position = 0