Coupler has a safety lock and a latching hook. The safety lock pivots between an unlocked position in which it does not contact a first implement pin receivable within a pair of apertures, and a locked position in which it retains the first pin within the apertures. The latching hook pivots between an unlatched position in which it does not contact a second implement pin receivable within another pair of apertures, and a latched position in which it retains the second pin within the apertures. A spring biases the safety lock toward the locked position, maintaining engagement of the safety lock with the first pin and preventing its withdrawal from the apertures in the event of a hydraulic system failure. When the implement is released, the spring continues to bias the safety lock toward the locked position, preventing withdrawal of the first pin from the apertures in the event of a hydraulic system failure before completion of the release operation.