diff --git a/lib/zlib.js b/lib/zlib.js
index 23f350d7b3..bbe09ef2c2 100644
--- a/lib/zlib.js
+++ b/lib/zlib.js
@@ -434,7 +434,7 @@ Zlib.prototype._transform = function(chunk, encoding, cb) {
   req.callback = callback;
 
   var self = this;
-  function callback(availInAfter, availOutAfter, buffer) {
+  function callback(availInAfter, availOutAfter) {
     if (self._hadError)
       return;