Canadians may be premature in celebrating the positive and conciliatory tone struck by U.S. President Donald Trump in his first face-to-face meeting with Canadian Prime Minister Justin Trudeau, warns a trade lawyer.

Canadian executives breathed a sigh of relief when Trump said he was only looking to “tweak” trade relations with Canada. But the word “tweak” can mean anything, according to Mark Warner, Principal at MAAW Law.

“I think yesterday we were being a bit too giddy when we heard the word ‘tweak,’” he told BNN in an interview.  “I don’t think this means we are out of the woods at all.”

Trump described the U.S. trade relationship as “outstanding” during a joint news conference with Trudeau. And while Trump railed against the North American Free Trade Agreement (NAFTA) during the election campaign and has continued to complain about the U.S. trade imbalance with Mexico, he said the country’s issues with Canada are “much less severe” than with Mexico.

But it will be difficult for the U.S. to address trade issues with Mexico without either impacting Canada or unravelling the entire NAFTA deal, said Warner. “I have a hard time understanding where you could make major changes for Mexico and minor changes for Canada,” he said.

Minor changes have been made to NAFTA in the past, but any major restructuring would need to be approved by the U.S. Congress, which would open up the entire agreement to renegotiation, Warner said. “All the people interested in softwood lumber, they are going to show up and talk to their congress people, and so all those dairy issues, those supply management issues fold back into the process,” he said. “We need to know what exactly [what] he means when he says tweak.”