diff --git a/message.go b/message.go
index 393b414..1137aa0 100644
--- a/message.go
+++ b/message.go
@@ -74,6 +74,9 @@ func (m *Message) Sender() (*User, error) {
 		user = &User{Self: m.Bot.self, UserName: m.FromUserName}
 		err = user.Detail()
 	}
+	if m.IsSendByGroup() && len(user.MemberList) == 0 {
+		err = user.Detail()
+	}
 	return user, err
 }