Ashton Kutcher's worried about his stepdaughter's friendship with Lindsay Lohan

If your 18-year-old daughter was hanging out with an older party girl, would you like it? Sources are saying that Rumer Willis's stepfather, Ashton Kutcher is worried about her blossoming friendship with Hollywood wild child, Lindsay Lohan.

Rumer, daughter of Demi Moore and Bruce Willis, and Lindsay have been pals for some time now, but have been spending even more time together lately. Earlier this month they attended parties together two nights in a row: the launch of T-Mobile Limited Edition Sidekicks and the American Cinematheque Awards. According to an insider for Life & Style Weekly, Rumer is thrilled to have gotten closer with Lindsay. "Rumer can't stop gushing about how cool Lindsay is. Rumer feels honored by Lindsay's attention."

But Ashton is afraid his stepdaughter's relationship with Lindsay is getting in the way of more important things. Kutcher is protective of Willis, who, along with her two other sisters, calls him M.O.D. (my other dad). Life & Style reports that he has suggested that Rumer should not see Lindsay any more. The reason for his decision? "Education is very important to Ashton and he's afraid Rumer will think partying is better than studying," a source told L&S.