Larry David’s mega-selling Broadway comedy “Fish in the Dark” is keeping it all in the “Seinfeld” family, with Jason Alexander set to step into the role currently played by Larry David for the play’s six-week extension into mid-July.

Alexander, who’s also appeared in David’s HBO series “Curb Your Enthusiasm,” will play Norman Drexel, the protagonist of David’s stage comedy about a death in the family. The rest of the production’s original cast — including Rita Wilson, Rosie Perez, Jayne Houdyshell and Ben Shenkman — will appear in the show throughout the extension.

“Fish in the Dark” racked up a massive $13.5 million advance before it began its first performance, and it’s posted heavyweight numbers at the box office since kicking off its run in February. Given the deep ties between David’s cult of fandom, “Seinfeld” and Alexander, the actor’s replacement casting looks primed to keep those sales figures aloft.

David exits “Fish in the Dark” on June 7 (the closing date of the original limited engagement), with Alexander picking up performances June 9 and sticking around until the extension’s current end date, July 19.