This article examines how the partisan turnout bias (i.e. turnout rate differences across districts that are linked to the partisan vote shares in those districts) changes over time in PR districted electoral systems. We argue that the bias after the founding election is the unintended consequence of parties and voters' strategic behaviors when they respond to the incentives provided by the electoral system. By looking at the case of Portugal, one of the countries with the largest variation in district magnitude, we find that the increasing asymmetry in turnout rates across districts makes the bias more severe as time goes by.