diff --git a/app/router/lua.go b/app/router/lua.go
index 6cf55d5f1..75da27ccc 100644
--- a/app/router/lua.go
+++ b/app/router/lua.go
@@ -30,9 +30,9 @@ func (r *Router) RegisterLua(L *lua.LState) {
 		module.RawSetString("LocalOS", lua.LString(runtime.GOOS))
 
 		module.RawSetString("PickOutbound", L.NewFunction(func(L *lua.LState) int {
-			tag, ok := L.Get(2).(lua.LString)
+			tag, ok := L.Get(1).(lua.LString)
 			if !ok {
-				L.ArgError(2, "balancer tag must be a string")
+				L.ArgError(1, "balancer tag must be a string")
 				return 0
 			}
 			balancer, found := (*r.balancers.Load())[string(tag)]
diff --git a/app/router/script_test.go b/app/router/script_test.go
index 7daeb868a..75f52db75 100644
--- a/app/router/script_test.go
+++ b/app/router/script_test.go
@@ -101,7 +101,7 @@ func TestRouterScriptRouting(t *testing.T) {
 		{name: "route", body: `return "lua-out", "lua-rule"`, wantTag: "lua-out", wantRule: "lua-rule", wantCalls: "2"},
 		{name: "no match", body: `return nil`, wantErr: common.ErrNoClue, wantCalls: "2"},
 		{name: "empty tag", body: `return ""`, wantErr: common.ErrNoClue, wantCalls: "2"},
-		{name: "balancer error", body: `local tag, err = router:PickOutbound("missing"); return tag, nil, err`, wantMessage: "not found", wantCalls: "2"},
+		{name: "balancer error", body: `local tag, err = router.PickOutbound("missing"); return tag, nil, err`, wantMessage: "not found", wantCalls: "2"},
 		{name: "string error", body: `return nil, nil, "blocked"`, wantMessage: "blocked", wantCalls: "2"},
 		{name: "invalid tag", body: `return false`, wantMessage: "outboundTag", wantCalls: "2"},
 		{name: "invalid rule", body: `return "lua-out", false`, wantMessage: "ruleTag", wantCalls: "2"},
@@ -202,7 +202,7 @@ func TestRouterScriptBalancerReload(t *testing.T) {
 	r := startLuaRouter(t, `
 local router = require("xray.router")
 function HandleRoute()
-    local tag, err = router:PickOutbound("balance")
+    local tag, err = router.PickOutbound("balance")
     return tag, "balanced", err
 end`, nil, config("old"))
 	pick := func(want string) {
@@ -236,7 +236,7 @@ func TestRouterScriptConcurrentBalancerReload(t *testing.T) {
 	r := startLuaRouter(t, `
 local router = require("xray.router")
 function HandleRoute()
-    local tag, err = router:PickOutbound("balance")
+    local tag, err = router.PickOutbound("balance")
     return tag, nil, err
 end`, nil, config("a"))