The expectant mom opened up to ET about her struggle to eat healthy on set.
Katherine Heigl is having a little trouble with the legal jargon on her new drama, Doubt, and the pregnant star says it's all because of her forthcoming bundle of joy and the resulting "pregnancy brain."
"Usually I'm pretty good at memorizing. I can do that pretty quickly. It's like the only thing I've got," Heigl joked with ET's Leanne Aguilera during a recent visit to the Doubt set. "So it's really been eye-opening to me to struggle with that."
She also places the blame for her cravings for sweets on her baby, laughing, "It's lovely actually because I feel absolutely no responsibility for my behavior at all. It's great."
WATCH: Katherine Heigl Glows While Showing Off Baby Bump on the Red Carpet
The 37-year-old expectant mom said she's "trying really hard to stop" eating junk food, and she's come up with a plan she hopes will work: "Just eat one donut a week. Just have one and then stop thinking about it."
However, shooting a TV show with a full catering spread of sweets and treats doesn't make it easy for her.
"If I'm not on set, I don't think about them that much. And I don't eat them because they're not around," Heigl explained. "But on set, crafty always has a plethora of donuts in really pretty pink boxes and I can't stop thinking about them."
WATCH: Katherine Heigl Talks Pregnancy, Says Her Daughters Are 'So Excited' for a Baby Brother
She's also come across another very challenging issue: hiding her growing baby bump. However, the production crew has come up with some very interesting ways to cover it up.
"Today was really impressive," Heigl shared. "I had to come up to my desk and I didn't know that they had strategically placed [a desk lamp]. They were like, 'Katie, would you mind taking a small step to your right?' And I looked down and this lamp was right there. That's clever."
Heigl and her husband, singer Josh Kelley, announced that they were expecting the new addition to their family back in June. The couple is planning to welcome their baby boy in January.
Doubt, which also stars Laverne Cox, Dule Hill, Steven Pasquale and Elliot Gould, debuts midseason on CBS.
WATCH: Pregnant Katherine Heigl Cradles Her Growing Baby Bump on the Set of 'Doubt'
