Production on the final season of TNT’s Falling Skies has halted after a security guard was killed on the set, EW confirmed.

On Monday night, a security guard was reportedly struck by an unattended truck rolling down a hill on the Vancouver-based production, Deadline wrote. “We are deeply saddened by this tragic event, and on behalf of the producers and TNT, we wish to express our heartfelt condolences to the family of the security guard,” TNT said in a statement. The accident is currently being investigated.

Falling Skies is shooting its 10-episode fifth and final season, which is expected to debut next summer.