diff --git a/include/xo/reflectutil/reflect_struct_info.hpp b/include/xo/reflectutil/reflect_struct_info.hpp
index 98313088..60c52392 100644
--- a/include/xo/reflectutil/reflect_struct_info.hpp
+++ b/include/xo/reflectutil/reflect_struct_info.hpp
@@ -6,6 +6,7 @@
 #pragma once
 
 #include <cstdint>
+#include <cstddef>
 
 namespace xo {
     namespace reflect {