diff --git a/tests/unit/face.t.cpp b/tests/unit/face.t.cpp
index 5fdfd1c..0ee95b4 100644
--- a/tests/unit/face.t.cpp
+++ b/tests/unit/face.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2022 Regents of the University of California.
+ * Copyright (c) 2013-2023 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -427,14 +427,14 @@
 
   BOOST_CHECK_EQUAL(face.sentNacks.size(), 0);
 
-  face.put(makeNack(*makeInterest("/unsolicited", false, nullopt, 18645250),
+  face.put(makeNack(*makeInterest("/unsolicited", false, std::nullopt, 18645250),
                     lp::NackReason::NO_ROUTE));
   advanceClocks(10_ms);
   BOOST_CHECK_EQUAL(face.sentNacks.size(), 0); // unsolicited Nack would not be sent
 
-  auto interest1 = makeInterest("/Hello/World", false, nullopt, 14247162);
+  auto interest1 = makeInterest("/Hello/World", false, std::nullopt, 14247162);
   face.receive(*interest1);
-  auto interest2 = makeInterest("/another/prefix", false, nullopt, 92203002);
+  auto interest2 = makeInterest("/another/prefix", false, std::nullopt, 92203002);
   face.receive(*interest2);
   advanceClocks(10_ms);
 
@@ -465,7 +465,7 @@
   face.setInterestFilter("/", bind([&] { hasInterest2 = true; }));
   advanceClocks(10_ms);
 
-  auto interest = makeInterest("/A", false, nullopt, 14333271);
+  auto interest = makeInterest("/A", false, std::nullopt, 14333271);
   face.receive(*interest);
   advanceClocks(10_ms);
   BOOST_CHECK(hasInterest1);
@@ -496,7 +496,7 @@
   face.setInterestFilter(InterestFilter("/").allowLoopback(false),
     bind([] { BOOST_ERROR("Unexpected Interest on second InterestFilter"); }));
 
-  auto interest = makeInterest("/A", false, nullopt, 28395852);
+  auto interest = makeInterest("/A", false, std::nullopt, 28395852);
   face.expressInterest(*interest,
                        bind([] { BOOST_FAIL("Unexpected data"); }),
                        [&] (const Interest&, const lp::Nack& nack) {