"The first time with [3-year-old son] Griff, I saw it and was like, 'Not a girl!' I caught it this time too," the actress, who is expecting her second son in September, tells PEOPLE.

During both of her pregnancies, Leigh-Allyn Baker was certain she was having a girl — until she spotted a certain telltale giveaway during her ultrasounds.

“The first time with [3-year-old] Griffin, I saw it and was like, ‘Not a girl!’ I caught it this time too,” the actress, who is expecting her second son in September, tells PEOPLE exclusively.

“I was really excited it was a boy. Even though I would love a little girl for me personally, I love being a mom to boys,” says Baker, who plays a mom of five on Disney Channel’s hit family sitcom Good Luck Charlie.

“And I kind of wanted Griffin to have a same-sex sibling. They’ll certainly have more in common, and it will be easier to develop a friendship when they’re the same.”

The big brother-to-be already has a strong opinion on at least one matter: the baby’s name.

“He wants to name the baby Myber,” says Baker, 40. “I don’t know where he got it. My husband [Keith Kauffman] and I will be in the other room discussing names and we’ll hear, ‘I said “Myber!”‘”

Of course, Mom and Dad get final say, and Baker reveals they’re leaning toward the name Jasper James.

“I fall for those names that are kind of traditional and have been around forever but are not on the Top 100 list,” she says.

Meanwhile, her alter ego Amy Duncan is delivering her fifth baby in a special one-hour episode of Good Luck Charlie airing Sunday at 8 p.m. ET on the Disney Channel. Baker revealed her real-life pregnancy to the cast and crew at the end of filming the episode.

“I said, “Now that we’ve had a baby, I guess I should tell you all, I’m pregnant,'” recalls Baker. “People laughed because they thought I was making a joke of the fact that Amy Duncan had so many kids. And I had to say, “No, I’m really pregnant!” They were really surprised and really happy.”

— Michelle Tauber