A coupler assembly for coupling a trailer to a towing vehicle hitch ball is provided. The assembly includes a housing with a coupler socket adapted to receive a hitch ball. A ball clamp is disposed within the interior of the coupler housing and is movable toward and away from the coupler socket. The ball clamp has a clamping portion that retains the hitch ball within the coupler socket with the ball clamp positioned toward the coupler socket in a hitch ball retention position. A guide ramp is disposed within the coupler housing rearward of the coupler socket. The guide ramp projects toward the ball clamp and slopes upward and forward toward the coupler socket. A lateral guide member is disposed on the ball clamp rearward of the guide ramp. The lateral guide member cooperates with the guide ramp surface to limit forward movement of the ball clamp into the coupler socket.