Mason Disick can't be cranky on Aunt Kim's big day!

Kim Kardashian's adorable nephew is supposed to be the ring bearer for her wedding to Kris Humphries on Saturday, but her sister Kourtney isn't so sure the tot will be able to perform his duties! 

Kourtney, 32, told Hollybaby at Wednesday night's launch bash for the Kardashian Kollection in Hollywood that the family is "planning on" Mason being a part of the bridal party.

"[But] we'll see what happens," she told Us Weekly. "He is 20 months old... We'll see if he behaves!"

Kourtney also admitted to Hollybaby that she "might be more nervous than Kim" and told her kid sister, 30, "I think I am going to have a heart attack!" 

Khloe, who said "I do" to Lamar Odom in 2009, is more relaxed about her sister's upcoming nuptials. Her advice for Kim? "At some point in your wedding, take your husband in a corner and just be quiet and look and enjoy the whole presence of it," she told Us.

The bride-to-be herself is "totally calm" about her wedding, and credited her 26-year-old NBA beau for helping ease her nerves. "We have a really good balancing system of, you know, our personalities," she told Us. "[Kris] lets me chill. He gives me my space when I need to design and approve shoes and clothes and everything, and I kind of do the same for him. We just have a good connection."