An assembly includes a vehicle seat having a seat bottom and a seatback supported by the seat bottom. The assembly includes an airbag supported by the seatback. The airbag is inflatable to an inflated position. The assembly includes a seatbelt webbing extending from the seatback to the airbag. The seatbelt webbing is between the airbag and the seatback in the inflated position. The assembly includes a pyrotechnic device supported by the seat bottom and operatively coupled to the airbag.