In 2017, the position became vacant for a period of 40 days, the only time in its history when it has been unoccupied. As part of the 2017–18 Australian parliamentary eligibility crisis, it emerged that the then-incumbent Barnaby Joyce was a citizen of New Zealand by descent ("jus sanguinis" – by right of blood) at the time of the 2016 federal election. Joyce told the House of Representatives that he was advised of his citizenship status on 10 August 2017 by the New Zealand High Commission and his renunciation of his dual citizenship became effective on 15 August 2017. Nevertheless, he asked for his case to be referred to the High Court of Australia (sitting as the Court of Disputed Returns) for adjudication, and they ruled that his election was invalid under section 44 of the Constitution of Australia. The government immediately issued writs for a by-election for the seat of New England to be held on 2 December 2017, which Joyce won easily. Governor-General Sir Peter Cosgrove re-appointed Joyce as deputy prime minister on 6 December 2017.