diff --git a/plugin.h b/plugin.h
index eb469f48..b3c296ea 100644
--- a/plugin.h
+++ b/plugin.h
@@ -14,6 +14,7 @@ See LICENSE for license details.
 #include <string>
 #include <string_view>
 #include <cstring>
+#include <optional>
 
 #include "logger.h"
 #include "acltree.h"