diff --git a/wxdata/source/scwx/network/ntp_client.cpp b/wxdata/source/scwx/network/ntp_client.cpp
index 0a340f87..e95599dd 100644
--- a/wxdata/source/scwx/network/ntp_client.cpp
+++ b/wxdata/source/scwx/network/ntp_client.cpp
@@ -5,6 +5,7 @@
 
 #include <condition_variable>
 #include <mutex>
+#include <optional>
 
 #include <boost/asio/ip/udp.hpp>
 #include <boost/asio/steady_timer.hpp>