Britney Spears has made two guest appearances on CBS’s How I Met Your Mother, and as far as Neil Patrick Harris is concerned, she’s welcome back any time.

“The door is open for her,” Harris told PEOPLE at an Academy screening of the show at McGee’s Bar & Grill in Manhattan. “We would love (guest stars) who get in the show’s world to stick around if they want to … but I don’t know what the writers have planned.”

Spears played Abby, a ditsy receptionist dating Barney (Harris’s character), but interested in Ted (Josh Radner’s character). Based on some foreshadowing in the script, the pop princess may very well return in season four, says Harris.

“I gave her the address to Ted’s apartment at the end of the last episode, so I wouldn’t be surprised if she showed up again,” he told PEOPLE.

During a Q&A post-screening, the cast reminisced about Spears’s time on set.

“Carter [Bays, the creator] had a great line at the table read. He introduces all the guest cast. He said, ‘And I hope I pronounce this correctly, ‘Britney Spears,’” Josh Radner told fans at McGee’s, the bar that helped inspire the series.

“There were wristbands that we wore on set, so that people didn’t come on to the set. In her world, people go up in the rafters and take pictures,” Harris said.

“We wanted to give her the freedom in a closed environment to be as free to act, and fail, and succeed as she wanted to because that’s the process of doing this,” he continued. “She was lovely, and those two weeks were actually quite swell for us.”

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