THE case of a woman from Hanau, in Hesse, shows why Kenan Kolat, leader of Germany’s Turks, calls the German citizenship law “absurdity cubed.” Born in Germany to Turkish parents, she was a dual citizen. According to the law, she had to relinquish one passport between her 18th and 23rd birthday. She chose to forgo the Turkish one. But the Turkish bureaucracy was slow, her birthday came—and her German citizenship went instead.

International law has never fully embraced multiple citizenship. Many countries frown on it, though others take a more relaxed attitude. Germany, however, manages to make it especially complicated for citizens of foreign origin. Its traditional approach goes back to a law passed before the first world war. Based on jus sanguinis (“right of blood”), it gave citizenship to anybody of German descent, but not to foreigners born in Germany, as countries such as America and France that practise jus soli (“right of soil”) do. Then, in 1999, a centre-left government added the two notions together. This would have let a woman born in Germany to Turkish parents be simultaneously German and Turkish. But that law coincided with a regional election in Hesse, where the centre-right Christian Democratic Union (CDU) seized on the issue to mobilise its conservative base in opposition. The CDU won the state and took control of the upper house, where it blocked the new law.

A compromise was reached in 2000. Children born in Germany to foreign parents after 1990 can get two passports but have to choose one citizenship before they are 23. This year, the first cohort of such children, about 3,300, reach that age. From 2018 the number will reach 40,000 a year or more. There are about half a million such cases all told, more than two-thirds of them of Turkish descent.

Yet not all young dual citizens must choose. A child born to a German parent in America, say, retains both passports for life. So does a child born to a Greek or Spanish parent in Germany, because dual citizenship is allowed for members of the European Union and Switzerland. This seems unfair to the Turks. This week Recep Tayyip Erdogan, the Turkish prime minister, said as much to Angela Merkel, Germany’s chancellor, during her visit to Turkey. (Mrs Merkel also explained that, though happy for Turkey’s EU accession talks to continue, she retained her “scepticism” about its ever becoming a member.)

Besides being unjust and creating two classes of citizens, the law is a nightmare to administer, says Ulrich Kober at Bertelsmann Stiftung, a think-tank. Because countries like Iran do not let citizens renounce their citizenship and others make it costly or difficult, German law in theory grants exceptions. But the rules are not clear, reckons Kay Hailbronner, a lawyer. To make the decisions even more arbitrary, the 16 German states process the paperwork, and each uses different forms.

What better way to irritate those citizens whom Germany’s politicians say they want to integrate? Mr Kober thinks Germany should simply allow dual citizenship. So do the centre-left parties hoping to replace Mrs Merkel’s government in September’s election, as well as the CDU’s coalition partner, the Free Democratic Party. It may yet happen.