Jon Hamm requested a scene change when Daniel Radcliffe wagged something "that looked way too much like a wand" at him during their new show.
The two stars appear in a new programme called Playhouse Presents: A Young Doctor's Notebook, in which Daniel plays a younger version of Jon's character.
Both actors were very aware that Daniel needed to remove himself from his famous Harry Potter character.
"No, but there was this one moment where Dan was pointing something at me that looked way too much like a wand," Jon laughed to the latest edition of UK InStyle magazine, when asked in Daniel taught him any tricks. "We were like, 'No, you'll have to do something else.'"
Jon was thrilled when he heard Daniel was interested in the TV show. He has admired the younger star's work for a long time.
"Getting him involved in our weird little project was a bit of a slam dunk for me," he said. "I mean, he's an international superstar and he totally threw himself into it."
Jon is best known for playing macho womaniser Don Draper in Mad Men. He finds a lot of his fans struggle to distinguish between him in real life and his on-screen character.
It doesn't bother him too much though as there are certain perks to the mix ups.
"They tend to buy me a lot of drinks. I find myself having to turn down many of them - no one can really drink as much as Don," he quipped.