diff --git a/CHANGES b/CHANGES
index f569c16..de63c86 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+2.0.4 2014-06-12
+- Fix worker master
+
 2.0.3 2014-06-11
 - Fix table encryption with UDP
 
diff --git a/shadowsocks/asyncdns.py b/shadowsocks/asyncdns.py
index cbdd6a5..f7934cb 100644
--- a/shadowsocks/asyncdns.py
+++ b/shadowsocks/asyncdns.py
@@ -423,7 +423,9 @@ class DNSResolver(object):
                 self._send_req(hostname, QTYPE_A)
 
     def close(self):
-        self._sock.close()
+        if self._sock:
+            self._sock.close()
+            self._sock = None
 
 
 def test():