diff --git a/src/challenge/challenge-email.cpp b/src/challenge/challenge-email.cpp
index 01bb7ba..c4de9ce 100644
--- a/src/challenge/challenge-email.cpp
+++ b/src/challenge/challenge-email.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2017-2022, Regents of the University of California.
+ * Copyright (c) 2017-2024, Regents of the University of California.
  *
  * This file is part of ndncert, a certificate management system based on NDN.
  *
@@ -19,6 +19,9 @@
  */
 
 #include "challenge-email.hpp"
+
+#include <ndn-cxx/util/logger.hpp>
+
 #include <regex>
 #include <boost/process.hpp>