There are bestsellers, and there’s Harry Potter.

Book sales fluctuate with the ebb and flow of the political climate, the latest fads in mindfulness, and praise from prize committees. But when it comes down to it, nothing really matters in book publishing except Harry Potter.

Sales data published Dec. 12 by industry magazine Publishers Weekly show that this year’s new Potter release, Cursed Child—Parts I and II, dwarfs all the rest. The title—not quite a book but a script based on a play about Harry Potter’s youngest son—has sold 4.18 million print copies in the US in five months. (Publishers Weekly gets their sales data from Nielsen BookScan, which accounts for about 80% of print sales from traditional publishers in the US.)

That’s nearly four times the next bestselling book, the paperback version of Paula Hawkins’s The Girl on the Train—even though both were released in July 2016, and this edition of Girl on the Train arrived with a movie tie-in starring Emily Blunt.

By comparison, in all of 2015 the top-selling fiction book was Harper Lee’s Go Set a Watchman, which sold about 1.6 million copies in print in the US. In nonfiction, Marie Kondo’s The Life-Changing Magic of Tidying Up sold 1.1 million copies.

Just for the week of Nov. 28, 2016, a new book in Jeff Kinney’s mega-selling Diary of a Wimpy Kid series, about a middle-school wuss, gave Cursed Child a run for its money, selling 108,090 units compared to 54,841. But it’s still not on pace for 4 million; last year the 10th book in the series sold about 1.5 million print units in the US.