A self-propelled material handler has a pivotally mounted boom on a frame, and a cab that is positioned adjacent the side of the boom. The cab has an operator's entrance and exit opening on a side of the cab, that is positioned to permit an operator to enter and exit the cab and sit on a seat in the cab. A lateral restraint bar is mounted between the seat and the cab opening, and is movable to a working position where it obstructs the cab opening so that portions of the operator cannot be moved outwardly through the cab side opening from the interior, and which pivots to a raised position to permit an operator to pass through the cab opening. When the restraint bar moves away from its working position, a signal is provided to disable machine controls.