diff --git a/src/challenge/challenge-module.hpp b/src/challenge/challenge-module.hpp
index a0c7b60..b3baefb 100644
--- a/src/challenge/challenge-module.hpp
+++ b/src/challenge/challenge-module.hpp
@@ -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.
  *
@@ -24,6 +24,7 @@
 #include "detail/ca-request-state.hpp"
 
 #include <map>
+#include <tuple>
 
 namespace ndncert {