A constitutional amendment procedure was initiated during the 18th legislature by the Five Stars Movement, to cut the size of both houses by more than a third (from 630 and 315 members, to 400 and 200). To avoid incompatibility with the proposed amendment, the 2019 law adapts the Rosatellum law, and sets fractions for each type of seat (proportional or majoritary) instead of exact numbers. The ratio of single-winner districts over the total number of seats in Rosatellum was equal to 3/8 in both houses, and the law 51/2019 retains those proportions.