diff --git a/lib/Connection.js b/lib/Connection.js
index 4afbd21..619862f 100644
--- a/lib/Connection.js
+++ b/lib/Connection.js
@@ -1710,7 +1710,7 @@ Connection.prototype._starttls = function() {
     });
 
     self._sock.on('error', self._onError);
-    self._sock.on('timeout', this._onSocketTimeout);
+    self._sock.on('timeout', self._onSocketTimeout);
     self._sock.setTimeout(self._config.socketTimeout);
 
     self._parser.setStream(self._sock);