diff --git a/src/net/dns.hpp b/src/net/dns.hpp
index 79d9a10..5e22a84 100644
--- a/src/net/dns.hpp
+++ b/src/net/dns.hpp
@@ -1,5 +1,5 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
+/*
  * Copyright (c) 2013-2017 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
@@ -22,17 +22,11 @@
 #ifndef NDN_NET_DNS_HPP
 #define NDN_NET_DNS_HPP
 
+#include "asio-fwd.hpp"
 #include "../util/time.hpp"
 
 #include <boost/asio/ip/address.hpp>
 
-// forward declaration
-namespace boost {
-namespace asio {
-class io_service;
-} // namespace asio
-} // namespace boost
-
 namespace ndn {
 namespace dns {