The parent of Office Depot rebuffed rival Staples’ plan to buy the company for $40 per share, but it’s willing to keep talking and could be open to an alternative tie-up.

ODP Corp. sent a letter to the private-equity owner of Staples on Tuesday morning, according to a person familiar with ODP’s response who wasn’t authorized to speak publicly. But while ODP will not accept the unsolicited takeover offer as is, it would be open to a joint venture or the sale of only a portion of its business, the person said.

The Wall Street Journal reported on the letter earlier.

Last week, closely held Staples, under the corporate name USR Parent Inc., sent a letter to ODP laying out a plan to buy the company in a deal valued then at about $2.1 billion.

A tie-up, even a partial one, would bring together two of the biggest names in office supplies at a time when brick-and-mortar retailers are trying to adapt. Sycamore Partners-backed Staples had previously tried to buy Office Depot, but the $6.3 billion acquisition was called off in 2016 due to antitrust scrutiny.