diff --git a/bot.go b/bot.go
index 9d6ef2f..3739f0d 100644
--- a/bot.go
+++ b/bot.go
@@ -189,8 +189,12 @@ func (b *Bot) RegisterMessageHandler(handler MessageHandler) {
 }
 
 // 当消息同步发生了错误或者用户主动在手机上退出，该方法会立即返回，否则会一直阻塞
-func (b *Bot) Block() {
+func (b *Bot) Block() error {
+	if b.self == nil {
+		return errors.New("`Block` must be called after user login")
+	}
 	<-b.exit
+	return nil
 }
 
 func NewBot(caller *Caller, storage WechatStorage) *Bot {