Abstract: A collapsible roll-over protection system is provided with an upper section pivotally connected to a fixed lower section by a four-bar linkage. The linkage permits the upper section to be pivotally rotated rearwardly of the lower section and lowered to an inoperative position adjacent to and immediately behind the lower section. The pivot linkage includes an apertured tab that registers with a locking opening on the lower section to fix the upper section in the inoperative position. The engagement surfaces of the upper and lower sections is slanted with respect to the axis of the legs of the upper and lower sections to facilitate the movement of the upper section between the operative and inoperative positions. A locking pin fixes the structure in both the positions to prevent loose parts whenever the structure is moved between positions.