Former Texas Gov. Rick Perry might have given Donald Trump a full-throated endorsement for president, but he is not so fond of the presumptive Republican nominee’s plan to build a wall along the U.S.-Mexican border.

In an exchange posted Monday with Snapchat’s Peter Hamby on the social network’s political show, “Good Luck America,” Perry shot down Trump’s proposal.

“I’m for Donald Trump, and he says we’re going to build a wall, the Mexicans are gonna pay for it,” he said. Hamby then injected, “It’s not going to happen.”

“Well, it’s not,” Perry agreed, adding it might not only in the literal sense. “It’s a wall, but it’s a technological wall, it’s a digital wall. There are some that hear this is going to be 1,200 miles from Brownsville to El Paso, 30-foot high, and listen, I know you can’t do that.”

During the early stage of this GOP presidential primary nominating contest last year, the real estate mogul made his proposal to build a border wall a centerpiece of his campaign. His controversial plan has been rebuked by both liberals and conservatives who have called it unrealistic. A recent poll by the University of Texas/Texas Politics Project found 52 percent of Texas registered voters said they either “strongly” or “somewhat” supported building a wall between the United States and Mexico.

Perry has long been a critic of building a wall or fence along the border. In 2011, during his first failed run for president, he called for “strategic fencing” along parts of the border.

“If you build a 30-foot wall from El Paso to Brownsville, the 35-foot ladder business gets real good,” Perry said at the time at a campaign stop in New Hampshire.