Kanye West and Kim Kardashian want a prenup.

The A-list couple plan to keep their financial assets separate when they tie the knot and have allegedly decided to sign a prenup.

According to gossip website TMZ, the contract was especially important to Kim, who was always advised to be responsible when it comes to her finances by her late father, attorney Robert Kardashian.

Despite their decision to separate their fortunes - with Kim rumoured to be worth $40 million and Kayne $90 million - the pair will reportedly set up a joint account for household expenses.

The 'New Slaves' rapper proposed to his reality star girlfriend on her 33rd birthday (21.10.13) this Monday, hiring out the entire AT & T park baseball stadium in San Francisco and a 50-piece orchestra for the occasion.

The romantic rapper is reportedly planning to personalise their upcoming nuptials by writing his own rhyming vows.

A source told Hollywood Life: ''This is very special to him and he wants to make sure everything goes down the way he wants it. He's already been writing his vows, too - that's how seriously he's taking it. It's not going to be anything corny. It's going to come straight from his heart and it's going to be real.

''It's going to rhyme, know that. That's just how he is. But it's going to be deep and once he's done writing them, and saying them to her, he's going to keep it tucked away in his wallet for the rest of his life.''

Kanye better stick to his end of the bargain since 'X Factor' USA judge Demi Lovato has jokingly threatened to hunt him down if he hurts her pal Kim.

She told E! News: ''I've told Kanye before that if he doesn't treat her well, I'm going to come after him. I've known Kim for years and she's been such a good friend to me during some really hard times. She deserves that Giants stadium!''