diff --git a/VM/include/lua.h b/VM/include/lua.h
index 2f93ad9..8e7d646 100644
--- a/VM/include/lua.h
+++ b/VM/include/lua.h
@@ -346,6 +346,8 @@ struct lua_Debug
  * can only be changed when the VM is not running any code */
 struct lua_Callbacks
 {
+    void* userdata; /* arbitrary userdata pointer that is never overwritten by Luau */
+
     void (*interrupt)(lua_State* L, int gc);  /* gets called at safepoints (loop back edges, call/ret, gc) if set */
     void (*panic)(lua_State* L, int errcode); /* gets called when an unprotected error is raised (if longjmp is used) */