How to: Fix Parallels installing MacOS beta from recovery

I had a weird experience with an Parallels MacOS vm on my MacBook Pro this week. By accident I stumbled upon a solution / workaround.

Background story

Earlier this year, I enrolled for the Mojave beta program, but reverted back to High Sierra (which my MBP 2017 came with). All was good. I could go into Disk Utility, wipe the disk and reinstall High Sierra from MacOS Utilities, and Mojave when I later installed the public release of Mojave. The funny thing was, when installing a Parallels vm from recovery, it would install Mojave beta.

I had almost given up fixing this, but I made a discovery on another MBP I was working on. I had upgraded to Mojave from High Sierra (which it also shipped with) on that MBP and reinstalled it multiple times as described above. But one time on this MBP, I restarted the machine right after wiping the disk. I though that I could go back into MacOS Utilities after the restart, but the Mac just asked for a internet connection and had a spinning globe on a black background. After a while, it jumped back into MacOS Utilities.

Guess what. Now the reinstall option had reverted to High Sierra! This Mac had Mojave before the last disk wipe. So I tried the same on my own MBP, which had the same result.

This solved my Parallels beta problem! Now I get High Sierra when installing a vm from recovery (even if i upgraded to Mojave again on the host).

The solution

So if you are getting beta images in Parallels, remove your Mac from the beta program (if you haven’t already), wipe your disk and restart.

To me it’s still a mystery why Parallels shows me High Sierra as the recovery OS when the host it self shows Mojave. But that is a case for a later troubleshooting session.