It was reported last week that macOS Big Sur has a serious issue that can result in data loss when users try to upgrade a Mac to the latest version of the operating system without enough space available. Apple has finally fixed the issue with a new build of macOS Big Sur 11.2.1, which properly checks if the disk has the required space before starting the upgrade process.

Mr. Macintosh first reported that several users were getting an error message when upgrading a Mac computer to macOS Big Sur, which caused the Mac to no longer boot — and the only solution was to delete some files from the internal disk via Target Disk Mode (which doesn’t work for some models) or to wipe the entire disk.

Apple says upgrading to macOS Big Sur for the first time requires at least 35.5 GB of available storage — and this doesn’t include the 13 GB macOS Big Sur installer. Unfortunately, even if your Mac does not have 35.5 GB of storage available, macOS will try to install the Big Sur update, and that’s when users may lose all their data.

Apple has quietly released a new build of macOS Big Sur 11.2.1 (20D75) that no longer lets users upgrade the operating system without having enough space available. Unfortunately, this doesn’t seem to fix the Macs that got stuck after the macOS Big Sur installation started.