Abstract: An anti-jackknifing device adapted for engagement between a tractor having a fifth wheel engaged with a trailer. The device features a pair of catch arms rotationally engaged to a mount with the tractor. The distal ends of the catch arms move between an engaged position in a horizontal path between two trailer mounted engaging components adapted to engage the distal end and a disengaged position out of the path. The distal ends of the catch arms may be pivotally mounted. The distal ends of the catch arms and the engaging components may also be shaped to cooperatively engage on contact. A control causes the catch arms to rotate thereby engaging the distal ends of the arms between the engaging components either automatically above a threshold speed or manually. This engagement limits the angle of the trailer to the tractor to a predetermined angle when trailer rotates on the fifth wheel causing the engaging components to contact the distal ends of the catch arms.