diff --git a/lualib/skynet/db/mysql.lua b/lualib/skynet/db/mysql.lua
index 440c2ebc..c082a36c 100644
--- a/lualib/skynet/db/mysql.lua
+++ b/lualib/skynet/db/mysql.lua
@@ -881,7 +881,7 @@ local function _prepare_resp(self,sql)
 end
 
 -- 注册预处理语句
-function _prepare(self,query)
+local function _prepare(self,query)
     local stmt = self.stmts[query]
     if stmt then
         return stmt