The parents of a stuntman killed on the set of "The Expendables 2" last fall are suing the film's producers and its stunt coordinator.

Zong Yu Liu and Tan Mei Bai filed a wrongful-death lawsuit on Thursday in Los Angeles Superior Court, claiming that unsafe working conditions on the set of the Sylvester Stallone actioner led to the death of their 26-year-old son, Kun Liu, who was killed during a stunt sequence in the Bulgarian capital of Sofia. Liu was performing in a boat sequence when he was wounded by a nearby explosion on Oct. 27.

Liu's parents are seeking unspecified damages of more than $25,000 from Nu Image/Millennium Films, along with the film's stunt coordinator, Chad Stahelski. The suit alleges that the filmmakers "negligently and carelessly failed to provide adequate protection from harm to the participants of the stunts."     

At the time of the accident, Bulgarian officials reported that another stuntman was seriously injured during the same explosion. Nu Image/Millennium Films released a statement in November, saying, "The filmmakers are working closely with the authorities in responding to and investigating this accident." The companies are not commenting on the suit.

Along with Stallone, "The Expendables 2" also stars Bruce Willis, Chuck Norris and Arnold Schwarzenegger, who is testing the waters for an action-hero comeback following his seven-year stint as governor of California. The film is slated for an Aug. 17 release date. None of the stars were mentioned in the suit.

Although stunt injuries are common on movie sets, deaths are said to be relatively rare. Few statistics regarding stunt fatalities are kept, but at least one report puts the number of deaths at 2.5 for every 1,000 stuntmen -- making stunt work the ninth most dangerous job in America, right behind police officer.