diff --git a/include/rtti/typeinfo.h b/include/rtti/typeinfo.h
index 9144977..ecf7304 100644
--- a/include/rtti/typeinfo.h
+++ b/include/rtti/typeinfo.h
@@ -68,6 +68,11 @@ typedef int (*obj_init_fn_t)(meta_obj_t*, va_list);
 typedef void (*obj_destroy_fn_t)(meta_obj_t*);
 
 /* lock/unlock */
+enum {
+    RTTI_LOCK_READ = 0,
+    RTTI_LOCK_WRITE
+};
+
 typedef int (*lock_fn_t)(meta_obj_t*, uint64_t);
 typedef void (*unlock_fn_t)(meta_obj_t*);