diff --git a/src/openrct2/core/Nullable.hpp b/src/openrct2/core/Nullable.hpp
index 4732af9ebe..130fc037f5 100644
--- a/src/openrct2/core/Nullable.hpp
+++ b/src/openrct2/core/Nullable.hpp
@@ -17,6 +17,7 @@
 #pragma once
 
 #include "../common.h"
+#include <cstddef>
 
 template<typename T>
 struct Nullable