diff --git a/src/leaf_data_type.hpp b/src/leaf_data_type.hpp
index 35a2961..c3c30c9 100644
--- a/src/leaf_data_type.hpp
+++ b/src/leaf_data_type.hpp
@@ -7,6 +7,7 @@
 
 #pragma once
 #include <memory>
+#include <optional>
 #include <set>
 #include <string>
 #include <variant>