Updated on May 26 at 4:57 p.m. ET

It could be yuge.

Presumptive Republican nominee Donald Trump said Thursday he’d be willing to debate Democratic hopeful Bernie Sanders before the June 7 California primary—but with a few conditions.

Trump only offered vague outlines about his terms, but repeatedly cited a charity component. “I’d love to debate Bernie, but they’d have to pay a lot of money for it,” he said during a press conference in North Dakota. He suggested raising between $10 and 15 million “for maybe women’s health issues or something.”

He added it should take place in a “big arena.”

It’s not clear where Trump wants the money to come from. In the past, he’s criticized the networks for reportedly cashing in on his presidential debate appearances with sky-high ad sales. In September, Trump wrote a letter to CNN president Jeff Zucker urging him to donate the proceeds to veterans’ charities.

Sanders first proposed the debate by writing a letter to the real-estate mogul to challenge him. While Trump appeared on ABC’s Jimmy Kimmel Live on Wednesday night, Kimmel read Sanders’ letter aloud: “Hillary Clinton backed out of an agreement to debate me in California before the June 7th primary. Are you prepared to debate the major issues facing our largest state and the country prior to the California primary?”