Article 4
This Protocol shall remain open for signature by the High Contracting Parties until 30 June 2012. This Protocol shall be ratified by the High Contracting Parties, and by the Republic of Croatia in the event that this Protocol has not entered into force by the date of accession of the Republic of Croatia to the European Union, in accordance with their respective constitutional requirements. The instruments of ratification shall be deposited with the Government of the Italian Republic. This Protocol shall enter into force if possible on 30 June 2013, provided that all the instruments of ratification have been deposited, or, failing that, on the first day of the month following the deposit of the instrument of ratification by the last Member State to take this step.