diff --git a/src/challenge/challenge-email.hpp b/src/challenge/challenge-email.hpp
index e2c7267..c5d76de 100644
--- a/src/challenge/challenge-email.hpp
+++ b/src/challenge/challenge-email.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
-/**
- * Copyright (c) 2017-2020, Regents of the University of California.
+/*
+ * Copyright (c) 2017-2021, Regents of the University of California.
  *
  * This file is part of ndncert, a certificate management system based on NDN.
  *
@@ -23,7 +23,6 @@
 
 #include "challenge-module.hpp"
 
-namespace ndn {
 namespace ndncert {
 
 /**
@@ -88,6 +87,5 @@
 };
 
 } // namespace ndncert
-} // namespace ndn
 
 #endif // NDNCERT_CHALLENGE_EMAIL_HPP