diff --git a/Reflection/Struct.hpp b/Reflection/Struct.hpp
index 761b878ec..36c74f6a8 100644
--- a/Reflection/Struct.hpp
+++ b/Reflection/Struct.hpp
@@ -12,6 +12,7 @@
 #include <cassert>
 #include <cstdarg>
 #include <cstring>
+#include <cstddef>
 #include <string>
 #include <typeindex>
 #include <typeinfo>