File this one under "no surprise here" -- Kim Kardashian and Kanye West are getting a pre-nup.

Although both of them are committed to the marriage and aren't actually worried about it falling apart, sources tell TMZ that they also realize that with their respective fortunes, it's just the smart thing to do.

And though they'll both hang onto their own money, TMZ adds that they've decided to create a big, fat joint account for living expenses and the such.