diff --git a/stl/inc/xkeycheck.h b/stl/inc/xkeycheck.h
index 6baa330a1fd..60ab98f3e21 100644
--- a/stl/inc/xkeycheck.h
+++ b/stl/inc/xkeycheck.h
@@ -6,7 +6,10 @@
 #pragma once
 #ifndef _XKEYCHECK_H
 #define _XKEYCHECK_H
-#include <yvals_core.h>
+
+// xkeycheck.h assumes that it's being included by yvals_core.h in a specific order.
+// Nothing else should include xkeycheck.h.
+
 #if _STL_COMPILER_PREPROCESSOR
 
 #if defined(__cplusplus) && !defined(_ALLOW_KEYWORD_MACROS) && !defined(__INTELLISENSE__)