diff --git a/include/aare/RawMasterFile.hpp b/include/aare/RawMasterFile.hpp
index 57d9db5..3908090 100644
--- a/include/aare/RawMasterFile.hpp
+++ b/include/aare/RawMasterFile.hpp
@@ -3,6 +3,7 @@
 #include <filesystem>
 #include <fmt/format.h>
 #include <fstream>
+#include <optional>
 
 #include <nlohmann/json.hpp>
 using json = nlohmann::json;