Mexico has long said it wouldn’t be paying for a border wall with the U.S. On Thursday, officials used some cheeky language on President Donald Trump’s favorite medium to reiterate their message.

Both Mexico’s Economy Minister Ildefonso Guajardo and the country’s chief Nafta negotiator Kenneth Smith rebuked Trump’s suggestion that gains from a new trade deal may be used to pay for a border wall with Mexico. That would mean the U.S.’s southern neighbor would indirectly be paying for part of the wall, Trump said in an interview with the Wall Street Journal.

“Mexico’s President has been very clear: Mexico will never pay for that wall,” Guajardo tweeted in Spanish.

A few minutes later, Smith, Mexico’s chief trade negotiator, tweeted in English “Let this be clear: the issue of the payment for a #border #wall is not, and will never be, part of the #NAFTA #negotiations #wearenotjoking.”

Shortly after Trump’s inauguration last year, plans for a meeting between the president and his Mexican counterpart Enrique Pena Nieto fell apart over the issue of paying for the wall. Negotiators from the U.S., Mexico and Canada are scheduled to meet for the latest round of Nafta talks in Montreal on Jan. 23.

Also Thursday, former Mexican President Vicente Fox took to Twitter to rebuke comments Trump had made about immigrants from Haiti, El Salvador and African nations.

Fox described Trump’s mouth using the same expletive Trump was said to have used to describe those countries. “America’s greatness is built on diversity, or have you forgotten your immigrant background, Donald?,” Fox added.