What is the ruling if a lease duration is specified using non-Islamic calendar systems?

Primary text

If the duration is specified as a Roman, solar, Persian, or Coptic year, and both parties are aware of the specific calendar used, the lease is valid, and the duration equals 365 days. This distinction arises because Roman months vary in length (seven have thirty-one days, four have thirty days, and one has twenty-eight days), while Coptic months are uniformly thirty days with an addition of five days to match the solar year. If one party is ignorant of the specific calendar, the contract is invalid due to the ambiguity of the duration for that party.