An air pressure actuated stop assembly (50) is disposed in at least one of first and second rotatably engaging housings of a coupling assembly (10), the housings (14) being affixed to ends of respective associated hoses 70) to complete an air passageway (24) therebetween when coupled. Each housing (14) has a portion with an exterior surface adjacent an interior surface of a complementary portion of the other housing (14) and rotatably slidable therealong during coupling and uncoupling of the assembly (10). The stop assembly (50) includes a spring biased pin (52) that moves when actuated by air pressure in the air brake hose (70) to a position to obstruct the path traveled by the portion of the opposite housing (14) in a direction uncoupling the two housings (14) thereby preventing rotational uncoupling of the housings (14) when the air brake system is pressurized. The pin (52) is automatically retracted when the air pressure is released thus permitting the housings (14) to be uncoupled.