diff --git a/src/decryptor.hpp b/src/decryptor.hpp
index edc6f2d..a8ea7c3 100644
--- a/src/decryptor.hpp
+++ b/src/decryptor.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019, Regents of the University of California
+ * Copyright (c) 2014-2022, Regents of the University of California
  *
  * NAC library is free software: you can redistribute it and/or modify it under the
  * terms of the GNU Lesser General Public License as published by the Free Software
@@ -25,8 +25,7 @@
 
 #include <ndn-cxx/face.hpp>
 
-namespace ndn {
-namespace nac {
+namespace ndn::nac {
 
 /**
  * @brief NAC Decryptor
@@ -44,7 +43,7 @@
   {
     bool isRetrieved = false;
     Buffer bits;
-    optional<PendingInterestHandle> pendingInterest;
+    std::optional<PendingInterestHandle> pendingInterest;
 
     struct PendingDecrypt
     {
@@ -111,7 +110,6 @@
   ContentKeys m_cks;
 };
 
-} // namespace nac
-} // namespace ndn
+} // namespace ndn::nac
 
 #endif // NDN_NAC_DECRYPTOR_HPP