Credit: Michael Kovac/FilmMagic

American Idol's Jason Castro better brush up on his lullabies.

The 24-year-old dreadlocked season 7 finalist announced on his blog Friday that he and wife Mandy Mayhall are expecting a baby girl in August.

"I am excited to announce that there will be a new addition to the Castro family!" the Dallas-based Castro -- who married Mayhall in January 2010 -- blogged. "We just found out yesterday that it is going to be a girl! haha that makes me laugh... what am i going to do with a sweet little girl?! probably just smile alot... i cannot wait!!!"

The singer also posted a photo of Mayhall's first sonogram, titled "The first picture of our little girl."

Castro's new full-length album, Who I Am, is in stores now.