China and Hong Kong will stop their domestic trading in ivory by the end of 2017 and by 2021, respectively. Hong Kong must speed up its ivory ban to avoid this mismatch, which leaves open a four-year window for smuggling ivory legally purchased in Hong Kong into mainland China. This will fuel sales in one of the world's largest ivory retail markets.

As a major ivory transit conduit where illegal ivory is laundered through legal retailers (see go.nature.com/2oby6jb), Hong Kong is designated by the Convention on International Trade in Endangered Species as a 'country of primary concern' (see go.nature.com/2ncroed). The annual 45 million visitors from mainland China account for 90% of ivory purchases in Hong Kong (go.nature.com/2njhb5z).

Now that Hong Kong has decided to ban the trade, we urge its government to coordinate with Beijing and align its plans with those of China.