The macOS Big Sur update has been causing some older MacBook Pros to get stuck on a black screen during installation, with no way that users can find to fix it. The issue seems to be most common on late-2013 and mid-2014 models of the 13-inch MacBook Pro. Owners of other Macs have reported Big Sur installation issues, too — and some say they’ve been able to fix those issues — but those two models of MacBook Pro seem to be having the most severe problems for now.

The issues were spotted by MacRumors, which saw complaints of frozen laptops in its forums, on Reddit, and on Apple’s support site. There’s no clear indication of what could be causing the problem, and simple ways of fixing it — like resetting NVRAM or booting in safe mode — either can’t be accessed or don’t resolve the issue, users have said.

Big Sur has had an unusual number of launch issues. High-demand for the update seems to have slowed Apple’s servers to a crawl, which has led to a widespread slowdown of newer Macs due to a little-known feature that verifies with Apple that apps don’t have malware before each time they run. The server issues also made it impossible for some users to install the update, with the OS showing an installation error as people tried to launch the installer.

Given the black screen problems some users have been having, perhaps the download issues were for the best. If you’re thinking about updating, it may be wise to give it a few weeks while the bugs are worked out. The Verge has reached out to Apple for comment.