Elon Musk took to Twitter early Saturday morning to announce that Tesla has delayed the rollout of its Full Self-Driving (FSD) software. 

“A few last minute concerns about this build,” Musk wrote. “Release likely on Sunday or Monday. Sorry for the delay.”

The news comes a year after Tesla began beta-testing the software, and just two days after Musk announced FSD would be rolled out to 1,000 drivers with perfect safety scores by midnight Friday. If everything goes well, the company will gradually release the software to drivers with scores of 99 or below. 

Of course, Tesla isn’t the first to express concern over the rollout of FSD. About three weeks ago, an official for the National Transportation Safety Board urged the automaker to address “basic safety issues” before expanding the software to more drivers.

“Basic safety issues have to be addressed before they’re then expanding it to other city streets and other areas,” Jennifer Homendy, chair of the TSB, told the Wall Street Journal in September. Homendy also criticized the company’s use of the term “full self-driving,” which she said was “misleading and irresponsible.” Homendy also said that Tesla “has clearly misled numerous people to misuse and abuse technology.”