diff --git a/EqSat/include/Luau/LanguageHash.h b/EqSat/include/Luau/LanguageHash.h
index 80bf8922..8c5f837c 100644
--- a/EqSat/include/Luau/LanguageHash.h
+++ b/EqSat/include/Luau/LanguageHash.h
@@ -1,6 +1,7 @@
 // This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
 #pragma once
 
+#include <cstddef>
 #include <functional>
 
 namespace Luau::EqSat