US television network CBS has warned stars attending the Grammys music awards show at the weekend not to reveal too much skin, including breasts, buttocks - or the dreaded "buttock crack".
In an email leaked to media outlets including celebrity news website TMZ, the television giant also warned of "puffy" bare skin exposure around the genital region.
"Please be sure that buttocks and female breasts are adequately covered," stated the letter from CBS's Standards and Practices department to representatives of stars due to take the stage in Los Angeles on Sunday.
"Thong-type costumes are problematic. Please avoid exposing bare flesh under curves of the buttocks and buttock crack.
"Bare sides or under curvature of the breasts is also problematic.
"Please avoid sheer see-through clothing that could possibly expose female breast nipples.
"Please be sure the genital region is adequately covered so that there is no visible 'puffy' bare skin exposure.
"Please avoid commercial identification of actual brand name products on T-shirts."
Janet Jackson famously suffered a wardrobe malfunction during the half-time show of the 2004 Super Bowl, flashing a nipple during a routine with Justin Timberlake.
The Federal Communications Commission (FCC) fined CBS a record $US550,000 for broadcasting the incident, but an appeal court later ruled that the broadcaster could not be held responsible for so-called "Nipplegate".
CBS did not immediately respond to requests for confirmation or clarification of the leaked Grammys letter.