Why i get double messages from historySync event

[tandem97]

i wrote a func to save messages:

func eventHandler(evt interface{}) {
	switch v := evt.(type) {
	case *events.Message:
		messageStorage.AddMessage(v.Info.Chat.String(), v.Info.Sender.String(), v.Message.GetConversation())
		fmt.Println("Received a message!", v.Message.GetConversation(), v.Info.Sender, v.Info.Chat)
	case *events.HistorySync:
		fmt.Println("Received a history sync")
		for _, conv := range v.Data.GetConversations() {
			for _, historymsg := range conv.GetMessages() {
				chatJID, _ := types.ParseJID(conv.GetId())
				evt, err := client.ParseWebMessage(chatJID, historymsg.GetMessage())
				if err != nil {
					log.Println(err)
				}
				eventHandler(evt)
			}
		}
	}
}

but i get some messages twice, why it happends?