Bookstore sales tumbled 10.9% this August compared to August 2016, according to preliminary figures released by the U.S. Census Bureau on Friday. Sales in August were $1.39 billion, down from $1.56 billion a year ago.

The decline is due in part to strong sales last summer of Harry Potter and the Cursed Child. August also includes sales from college stores as students start the fall semester and the decline likely reflects lower sales in those outlets. (August is typically the first or second biggest month for bookstore sales).

The large decline in August led to a 2.5% drop in bookstore sales in the first eight months of 2017 compared to the same period in 2016. Sales in the January-August span were $7.12 billion, down from $7.30 billion in the same period in 2016.

Sales for the full retail market were up 3.8% in August and increased 4.0% in the year-to-date.