Mac OS · macOS
Fix ‘An Error Occurred While Preparing the Installation’ on Mac
Source-checked About 10 minutes
Answer
Check free storage and internet access, delete a damaged installer, retry in safe mode, then install from macOS Recovery and repair the startup disk if the error persists.
Protect your data
Back up the Mac before deeper repairs. Record the full message and the macOS version being installed.
Check space and network
Open System Settings > General > Storage, free the space requested by the installer, and use a stable internet connection without a captive portal.
Download a fresh installer
Delete an installer that macOS says is damaged or unverifiable and download a compatible copy through Software Update or Apple's supported download page.
Try safe mode or Recovery
Retry Software Update in safe mode, or start macOS Recovery and choose Reinstall macOS. Reinstallation normally preserves data, but a backup is still essential.
Repair the startup disk
From Recovery, run Disk Utility First Aid. Erasing the Mac or restoring firmware is a last resort and should follow Apple's exact model-specific guidance.
Video walkthrough
If it does not work
- If installation still fails, preserve the exact stage and installer log, verify storage and compatible macOS, and use Apple recovery guidance without erasing first.
Sources and verification
Checked against official documentation on . Scope: macOS.
Reviewed against the linked first-party guidance; interface labels can vary by current app, service, or operating-system version.