Advocates of proportional representation in Canada tend to be supporters of parties that would benefit if our electoral system switched from the current first-past-the-post system to a system that allocates at least some seats based on parties’ popular vote. But what’s sauce for the goose is, unfortunately, also sauce for the gander, as the results from yesterday’s federal elections in Germany remind us.

Germany elects its Bundestag by a mixed-member system that combines members elected via single-member constituencies in a first-past-the-post system with additional members elected by state-level party lists. Each voter gets two ballots: a constituency ballot and a list ballot. When a party wins fewer seats via the constituency ballot than its popular vote would entitle it to, additional members are added from the party list.

In yesterday’s election, those list votes enabled not only the Greens (Bündnis 90/Die Grünen) and the Left Party (Die Linke) to go from one and five seats to 67 and 69 seats, respectively, it also allowed the centrist FDP to re-enter the Bundestag with 80 seats: despite getting nearly 3.2 million constituency votes, the FDP failed to elect a single member via the constituency ballot, whereas FDP lists got nearly five million votes.

But the German system also enabled the far-right Alternative für Deutschland to add 91 seats to the three seats elected via the constituency ballot. And here’s the problem: that which gives smaller centrist, leftist and environmentalist parties a voice in national politics also enables the extreme right.

In favour of an electoral system because you think it’ll benefit your side? Be careful: any system you create can also be turned by your opponents to their advantage.