Jessica Simpson has taken to poisoning her Ashlee Simpson’s mind against marriage in a transparent effort to keep her younger sister to making it to the altar with fiance Pete Wentz.

Star Magazine reports:

Jessica has even tried to talk Ashlee out of walking down the aisle with Pete, 28…She arranged a sister-to-sister heart-to-heart warning Ashlee that she was rushing into things with Pete, who has publicly talked about his former drug addictions and suicidal tendencies.

But Ashlee won’t be moved. Jess is going to have to get up pretty early in the morning to pull one over on ole baby sis; guess all Simpsons don’t have a stupid gene, after all:

“Jessica insists she’s very concerned, but Ashlee thinks she’s just jealous of her happiness. She thinks Jess is just trying to plant seeds of doubt in her head so that she second guesses the engagement,” the tabloid insider says.