Abstract: An improvement in a bicycle lock extends the ability of an existing bicycle lock of the type having a U-shaped shackle to secure a bicycle to a post, against theft, by slipping a generally U-shaped essentially rigid link over a leg of the U-shaped shackle of the existing bicycle lock, subsequent to locating the rear wheel of the bicycle in the link, so that upon locking the bicycle frame and front wheel of the bicycle to the post with the U-shaped shackle, the existing bicycle lock also secures the rear wheel of the bicycle against theft.