Sandra Bullock revealed the "inappropriate" Halloween costume her son picked out for her, during her appearance on "The Tonight Show with Jimmy Fallon" on Wednesday.

The 51-year-old actress told the late night host that she let her 5-year-old son Louis decide their costumes, according to People.

"We usually match, but this year he sort of deviated off the matching," Bullock said.

Bullock's said her son is planning on going as a Ninja Turtle for this year's holiday, but he chose a "Slutty Batgirl" costume for his mother.

"It was like the most inappropriate thing," she said. "You know how there's regular Batgirl, and then there's the ones for those moms that like to really turn it out? Like a little leather skirt, and the boots that go over the knee, and a bustier?"

The actress, who assured Fallon she wasn't going to wear the get-up, said the costume caught her son's eye as they were looking through a costume catalog together.

"He went, 'Mama, you hasta wear this!'" Bullock said. "And I went, 'No, mama doesn't hast to. I'm not wearing that around your friends.'"

Instead of her son's choice, Bullock said she plans to dress as either a pirate wench or a mime.

During a comedy sketch on the late night show, Bullock also talked to Fallon about their time working together on the Canadian soap opera, "Jacob's Patience." Fallon spoke about acting alongside Bullock, describing how she was difficult to work with because she refused to use her own arms.

The pair then recreated a scene from the fake show, which involved Bullock working in an ice cream parlor. Both host and guest used mannequin arms, as Bullock prepared the ice cream for Fallon's order. As the sketch went on, things got messy with hot fudge, sprinkles and ice cream all over everything, and Bullock even lost one of her fake hands while assembling the ice cream.

Bullock can next be seen in "Our Brand Is Crisis" on Friday, Oct. 30.