The effects of Britain’s vote to leave the European Union could hurt U.S. exports, now facing the headwinds of a strengthening dollar.

That’s according to Joe Vaclavik of Standard Grain, who cautioned that there could be cancellations of U.S. export contracts if the U.S. dollar surges higher.

The markets are already swooning. At midday, December corn futures were down 6 cents and November soybeans were down 21 cents. Wheat also slipped, falling 6 cents for September contracts.

“With the Brexit vote, what is going on with grains is a kind of kneejerk reaction to sell off commodities because of the higher dollar,” said Standard Grain’s Joe Vaclavik in his daily commentary.

Click here to listen to his full commentary.