CALL it Project Prenup! “Project Runway” host HEIDI KLUM has agreed to marry her bodyguard boyfriend Martin Kirsten, sources say, but only if he signs an ironclad prenuptial agreement that gives him absolutely nothing!

“Martin and Heidi had a huge fight after she said she probably wouldn’t get married again,” said a source close to her.

“But Heidi doesn’t want to lose Martin because she loves him, and so do her kids.”

The “AMERICA’S GOT TALENT” judge, 40, and Martin, 45, have exchanged gold “promise” rings, but sources say Heidi won’t walk down the aisle a third time unless Martin signs a strict agreement to keep him from touching a penny of her $70 million fortune.

“That’s all held in trust for her family,” said the insider.

Heidi has a daughter, Leni, 9, from a previous relationship, and Henry, 7, Johan, 6, and Lou, 3, with ex-husband Seal.

Celebrity divorce attorney Raoul Felder says Heidi needs the mother of all prenups due to the enormous difference between her net worth and Martin’s.

“Heidi can’t gamble with this,” Felder told The ENQUIRER. “She’ll have to make sure Martin has a lawyer so he can’t claim later that he didn’t know what he was doing.

“Secondly, she’ll have to make him sign a complete waiver of any interest in her wealth, fortune or support payments.”

Another source added: “Heidi’s not stupid. There’s no way she’s going to let a bodyguard sweep her off her feet and then clean out her bank account.”