diff --git a/include/ntdef.h b/include/ntdef.h
index 92366c3f3bb..8d04f83da5d 100644
--- a/include/ntdef.h
+++ b/include/ntdef.h
@@ -84,4 +84,6 @@ typedef struct _RTL_BALANCED_NODE
 
 #define RTL_BALANCED_NODE_RESERVED_PARENT_MASK 3
 
+#define RTL_CONSTANT_STRING(s) { sizeof(s) - sizeof(s[0]), sizeof(s), (void*)s }
+
 #endif /* _NTDEF_ */