diff --git a/obj.go b/obj.go
index e398276..c048eb3 100644
--- a/obj.go
+++ b/obj.go
@@ -515,8 +515,8 @@ func getObjItemID(c string, n string) int64 {
 }
 
 func silentGetObjItemID(code string, name string) int64 {
-	c := string.ToLower(code)
-	n := string.ToUpper(name)
+	c := strings.ToLower(code)
+	n := strings.ToUpper(name)
 	if v, ok := cacheObjItem.Load(c); ok {
 		i := v.(ChatWarsItem)
 		return i.ObjID64