As Sherritt International, the Canadian conglomerate that has been a close business partner of the Castro brothers for many years, has just discovered.
The publicly-listed Sherritt has confirmed that it received news on Friday that Cuba is "revoking" a 16-year-old agreement with the company and another Canadian partner relating to petrol exploration and production in waters off Cuba’s north coast.
The news has been received badly by the market, with millions of dollars worth of value in Sherritt wiped out over the past 24 hours.
And as usual, the Cubans have not explained why they are suddenly breaking their contract, which was not due to expire until 2018.
In fact, the only good news for the Canadians is a promise by the Castro brothers to pay USD140 million in compensation.
Well, that's the promise, anyway ...