Donald Trump cast further doubt on his upcoming summit with North Korea’s Kim Jong-un today, telling reporters, “it may not work out.” The summit was planned to take place on June 12.

“If it doesn’t happen, maybe it will happen later,” he said at a meeting with South Korean president Moon Jae-in, according to a White House pool report. After the meeting’s date and location in Singapore were set, both sides have stalled over the question of whether North Korea will commit to complete denuclearization.

“You never know about deals,” Trump said of the hurdles. “I’ve made a lot of deals. You never really know.” The comment echoes a sentiment Trump aired in his co-authored book The Art of the Deal, as New York Times columnist Andrew Ross Sorkin points out (paywall). “I never get too attached to one deal or one approach,” Trump wrote. “I keep a lot of balls in the air, because most deals fall out, no matter how promising they seem at first.”

Trump told reporters they will “know soon” about whether the summit happens. He refused to say whether he had spoken directly to Kim, but called North Koreans “hardworking, great people” and added that Kim “will be extremely happy” if the deal works out, according to the pool report.