diff --git a/tests/unit/security/validator-null.t.cpp b/tests/unit/security/validator-null.t.cpp
index 9d04cb8..8fc5a5e 100644
--- a/tests/unit/security/validator-null.t.cpp
+++ b/tests/unit/security/validator-null.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2020 Regents of the University of California.
+ * Copyright (c) 2013-2021 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -28,6 +28,8 @@
 namespace security {
 namespace tests {
 
+using std::bind;
+
 BOOST_AUTO_TEST_SUITE(Security)
 BOOST_FIXTURE_TEST_SUITE(TestValidatorNull, ndn::tests::KeyChainFixture)