The Swedish pop group Abba mainly wore its flamboyant outfits during its heyday in order to be able to take a tax deduction on its clothing, according to a new book.

One of the band members, Bjorn Ulvaeus, revealed in “Abba: The Official Photo Book,” that the group would not have been able to deduct the cost of its costumes, under Swedish tax laws, unless the clothing was so outrageous that it could not be worn on the street in normal life.

“In my honest opinion we looked like nuts in those years,” Ulvaeus wrote, according to The Guardian. “Nobody can have been as badly dressed as we were.”

Nevertheless, the band had a string of chart-topping hits in the 70s and 80s that are still widely performed today, including “Waterloo,” “Dancing Queen” and of course “Mamma Mia,” spawning the long-running Broadway musical.

Despite the group’s success with trend-setting fashions and music, Ulvaeus nonetheless did have some run-ins with the tax authorities. In 2007, he was accused of failing to pay 85 million kronor (or about $13 million) in Swedish taxes between 1999 and 2005, but he won the case on appeal, vindicating both him and his accountants.