Jennifer Aniston apparently didn't see the funny side of boyfriend John Mayer's joke about cheating on her.

During a recent show, the singer told the crowd that he had been unfaithful in his sleep.

"He was talking about 'dream cheating,' said an eyewitness. “He apparently made out with some chick in his dreams."

Insiders say that Jen “wasn't happy” on hearing about her man's light-hearted admission.

“One of the things that causes tensions between them at times is the jokes John makes when Jen isn’t around," said a source.

"She wasn’t happy when he told the audience at his show in California on July 26th that he had a dream he had ‘made out’ with someone other than her."

The couple have been dating for three months - and, if you believe the latest reports, are already talking marriage and babies.

Here's a glowing Jen visiting a pal in L.A. yesterday