A lock that includes a frame which is arranged to be secured on the outside against a first side of a tubular member of a hinged gate and at least one bolt which is arranged to extend through the tubular member, out of a second side thereof, into the keeper device. The keeper device is mounted on a fixed member, which is usually a pole arranged in the ground. In order to make it more difficult to force the gate open by inserting, for example, a crowbar between the gate and the fixed member, the lock and keeper set comprises a security device arranged to prevent the gate and the fixed member from being forced apart sufficiently to disengage the bolt from the keeper device. This security device includes a first security piece arranged to be secured to the frame of the lock and to project from the second side of the tubular member to extend, in the closed state of the gate, behind a second security piece on the keeper device.