diff --git a/apisix/kms/vault.lua b/apisix/kms/vault.lua
index 1343002fcb20..aa1eda425c20 100644
--- a/apisix/kms/vault.lua
+++ b/apisix/kms/vault.lua
@@ -28,7 +28,12 @@ local rfind_char = core.string.rfind_char
 
 local _M = {}
 
-
+-- This code is copied from apisix/core/vault.lua.
+-- The functions in apisix/core/vault.lua are currently only used in the jwt-auth plugin,
+-- and it is not suitable to be placed in the core module of APISIX.
+--
+-- When KMS is fully functional, we will remove apisix/core/vault.lua.
+--
 local function make_request_to_vault(conf, method, key, data)
     local httpc = http.new()
     -- config timeout or default to 5000 ms