diff --git a/core/otto.go b/core/otto.go
index 2508102..c3835c3 100644
--- a/core/otto.go
+++ b/core/otto.go
@@ -146,7 +146,7 @@ func init() {
 				v, _ := otto.ToValue(s.Get(int(i - 1)))
 				return v
 			}
-			GetUserName := func(_ otto.Value) otto.Value {
+			GetUserName := func() otto.Value {
 				v, _ := otto.ToValue(s.GetUserName())
 				return v
 			}