diff --git a/tools/ping/server/main.cpp b/tools/ping/server/main.cpp
index dcce849..d43f1d2 100644
--- a/tools/ping/server/main.cpp
+++ b/tools/ping/server/main.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2015-2019, Arizona Board of Regents.
+ * Copyright (c) 2015-2021, Arizona Board of Regents.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -26,6 +26,11 @@
 #include "ping-server.hpp"
 #include "tracer.hpp"
 
+#include <boost/asio/signal_set.hpp>
+#include <boost/program_options/options_description.hpp>
+#include <boost/program_options/parsers.hpp>
+#include <boost/program_options/variables_map.hpp>
+
 namespace ndn {
 namespace ping {
 namespace server {
diff --git a/tools/ping/server/ping-server.hpp b/tools/ping/server/ping-server.hpp
index 46df6f9..f13769c 100644
--- a/tools/ping/server/ping-server.hpp
+++ b/tools/ping/server/ping-server.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2015-2019,  Arizona Board of Regents.
+ * Copyright (c) 2015-2021,  Arizona Board of Regents.
  *
  * This file is part of ndn-tools (Named Data Networking Essential Tools).
  * See AUTHORS.md for complete list of ndn-tools authors and contributors.
@@ -25,6 +25,8 @@
 
 #include "core/common.hpp"
 
+#include <ndn-cxx/util/signal.hpp>
+
 namespace ndn {
 namespace ping {
 namespace server {
@@ -55,12 +57,12 @@
    *
    * @param name incoming interest name
    */
-  signal::Signal<PingServer, Name> afterReceive;
+  util::Signal<PingServer, Name> afterReceive;
 
   /**
    * @brief Signals when finished pinging
    */
-  signal::Signal<PingServer> afterFinish;
+  util::Signal<PingServer> afterFinish;
 
   /** @brief starts ping server
    *