diff --git a/lualib/skynet/inject.lua b/lualib/skynet/inject.lua
index 3c945ffe..f3ef65d2 100644
--- a/lualib/skynet/inject.lua
+++ b/lualib/skynet/inject.lua
@@ -1,5 +1,5 @@
 local function getupvaluetable(u, func, unique)
-	i = 1
+	local i = 1
 	while true do
 		local name, value = debug.getupvalue(func, i)
 		if name == nil then