The late summer swoon at the box office — no breakout hits since July, no decent opening weekend since “The Butler” — continues as Vin Diesel’s “Riddick” opened weak Thursday night and Friday and is headed for a $17-18 million weekend.

Not exactly a healthy start for a sci-fi film, an established (albeit, dated) franchise and a “star” who seemed to have gotten his mojo back.

“The Butler” is hanging around and closing in on $100 million (it’ll be in the 90s by the time the weekend ends).

“Instructions Not Included,” Pantelion’s Spanish language comedy, is in third place and doing another $5 million or so this weekend.