diff --git a/lib/zlib.js b/lib/zlib.js
index 1151b2cb88..82b08018e7 100644
--- a/lib/zlib.js
+++ b/lib/zlib.js
@@ -444,10 +444,9 @@ Zlib.prototype.flush = function(kind, callback) {
     if (callback)
       this.once('end', callback);
   } else if (ws.needDrain) {
-    var self = this;
-    this.once('drain', function() {
-      self.flush(kind, callback);
-    });
+    if (callback) {
+      this.once('drain', () => this.flush(kind, callback));
+    }
   } else {
     this._flushFlag = kind;
     this.write(new Buffer(0), '', callback);