Charlie Day and Mary Elizabeth Ellis
07/23/2011 AT 06:45 PM EDT
It's been a good year for comedian Charlie Day. His film Horrible Bosses
is a hit at the box office, and he's going to be a dad.
"We've got a kid due in December," Day, 35, confirmed to PEOPLE at a Maxim and FX party at San Diego Comic-Con Friday night. "We're five months along, and she's feeling great. We're excited."
Day and his wife Mary Elizabeth Ellis, 32, who stars alongside the actor as "The Waitress" on It's Always Sunny in Philadelphia
, consciously decided to expand their family, says the comedian.
"We decided now is the time, and we were fortunate that it happened," he says.
The duo shares the small screen with another real life couple, Kaitlin Olson and Rob McElhenney, who themselves became first-time parents
to son Axel Lee last September. According to Day, their costars have been generous with the parenting tips.
"People are always willing to give you free advice when you have a baby on the way, so we've gotten more than our fair share – and honestly, we're gonna need it!" he says with a laugh.
Thankfully, the parents-to-be will be on shooting hiatus when their first child is due to make its arrival.
"It's going to time out perfectly," Day explains. "We live in L.A., [so] my East Coast family and her Southern family may have to come see us this Christmas."