diff --git a/lib/compress.js b/lib/compress.js
index b7a59ae9..cace6f68 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -103,7 +103,7 @@ merge(Compressor.prototype, {
     }
 });
 
-(function(undefined){
+(function(){
 
     function OPT(node, optimizer) {
         node.DEFMETHOD("optimize", function(compressor){