Calvin Harris has only one rule on girlfriend Taylor Swift: don't write songs about him when they split.

According to Daily Mirror, Taylor Swift has cashed in on songs that she made about her ex-boyfriends.

"But that is all about to change for Taylor Swift as her current boyfriend - Calvin Harris -has put his foot down on any such antics," it said. "The DJ has reportedly banned her from writing songs about him because he feels it 'demeans' her."

The source told the tabloid, "It was the white elephant in the room, but it's been on his mind, so he confronted her about it last week, telling her he doesn't want her to do that to him."

Apparently, Calvin Harris "doesn't want to join the ranks of Swift refugee boyfriends who've been humiliated by one of her revenge songs."

Meanwhile, Ed Sheeran expressed his support for Taylor Swift and Calvin Harris.

In an interview with ZM, the Grammy winner said of Calvin Harris, "He's cool. He's a really nice guy. A really, really nice guy."

"Yeah, I'd give the seal of approval ... There are certain people that are just nice people in the industry," he said. "So yeah - I met him probably a year ago ... yeah - good guy. Really, really good guy."

Calvin Harris has reason to be worried about girlfriend Taylor Swift's penchant to write songs about past relationships.

Billboard magazine even listed the songs that Taylor Swift wrote about her ex-boyfriends.

The magazine said that Taylor Swift wrote "I Knew You Were Trouble" about Harry Styles; "Begin Again" about Connor Kennedy; and "The Last Time" dedicated to Jake Gyllenhaal.

Taylor Swift explained to NPR that the song, "The Last Time," is about her experience "with someone who was kind of this unreliable guy. You never know when he's going to leave, you never know when he's going to come back, but he always does come back."