Finland will grant extradition of its nationals only under the following conditions: at the discretion of the Ministry of Justice, a Finnish national may be extradited to a Member State of the European Union to stand trial for a crime the most severe punishment for which, under Finnish law, is at least four years imprisonment if committed under similar circumstances in Finland; a condition of extradition is that, once the judgement has become final, the requesting Member State undertake immediately to return an extradited Finnish national to Finland for possible imprisonment if he consents to serve his sentence in Finland; no Finnish vessel on the high seas or in a Finnish aircraft; no Finnish national may be prosecuted or punished for a crime other than that referred to in the application for extradition, without the authorisation of the Ministry of Justice; no Finnish national may be re-extradited to another State.