ANN ARBOR, Mich. — Borders Group Inc., the nation’s second-largest bookseller, said Tuesday it widened its net loss in the second quarter on heavy charges despite a boost in revenue from sales of the seventh book in the Harry Potter series.

For the quarter ended Aug. 4, the company reported a loss of $25.1 million, or 43 cents per share, versus a loss of $18.4 million, or 29 cents per share, in the prior-year quarter.

The company said excluding charges for a tentative agreement to settle litigation in California, store closure and relocation costs, executive severance costs, and professional fees, it had a loss of 26 cents per share for the quarter.

Analysts polled by Thomson Financial expected a loss of 34 cents per share.

Revenue rose 10 percent to $956.7 million from $866.3 million. Analysts predicted revenue of $916.4 million.

The company said its same-store sales at its domestic Borders Superstores rose 4.6 percent while its Waldenbooks Specialty Retail same-store sales climbed 6.2 percent. International same-store sales grew 8.2 percent.

Same-store sales, or sales at stores open at least a year, are a key indicator of retailer performance since they measures sales at existing stores rather than newly opened ones.

The company said its same-store sales growth was led by record sales of “Harry Potter and the Deathly Hallows,” the seventh and final book in the Harry Potter series.

Borders shares fell 91 cents, or 5.8 percent, to close at $14.80. The stock has ranged from $13.72 to $24.19 over the past year.