How to Fix a Damaged macOS Installer

Creating a macOS installer on a bootable USB drive provides a convenient way of installing a fresh copy of macOS on multiple Macs, and also allows you to perform a clean installation quickly and easily.

Catalina

If you tried to run your installer recently and unexpectedly received an error that it is damaged and can't be used, then don't worry – keep reading for a simple and straightforward way to fix it.

Why is my macOS Installer Damaged?

If you tried to use a macOS installer in the last few days or weeks, you may have been met with an error message saying something like "This copy of the Install macOS Mojave.app application is damaged, and can’t be used to install macOS."

As Apple explains in a newly published support document, the likely reason for the "damaged" error message is an expired certificate. Happily though, the fix is very simple.

How to Fix a Damaged macOS Installer

To fix the damaged installer, you should just download the installer again. Doing so will also ensure that you have all of the macOS updates that have been released since you made the original installer, meaning you won't have to update macOS immediately after the initial installation is complete.

You can find the latest official download links below for the last six versions of Apple's Mac operating system, all of which contain a new certificate that has not expired:

To learn how to perform a clean installation of macOS using the bootable USB drive method, click one of the following links: macOS Catalina, macOS Mojave, macOS Sierra.

Related Roundup: macOS Catalina

Top Rated Comments

(View all)

gank41

13 weeks ago

That message does not mean you can't download it.
It only means that the installer won't run on that system version.
You will see that message after the download is complete (because the system automatically tries to launch the installer)
And, you have the downloaded installer, in your Applications folder. I would save the installer app to an external drive, and use one of the methods to create a fresh bootable installer from that app.
Finally, delete the downloaded installer from your boot drive.

Actually, I get that message BEFORE it tries to download it. I'm well aware that you can still download the file and create USB Installers and whatnot.. Gotta have the file downloaded first, though. And I'm not able to get that far.

Rating: 4 Votes

chrfr

8 weeks ago

I am sure that I already had been looking and can't seem to find and it's puzzles me..

It could be on any drive attached to your computer.

Rating: 2 Votes

gank41

12 weeks ago

Right this had baffled me and a colleague for a few days. The issue im having, now I understand the cause of the error, is that the links send you to the App Store and it just announces that it cant connect to the store. It will if I go to an app thats there. Any clues folks

The only way I was able to get the App Store installers was by going through a Virtual Machine of 10.14 and downloading them from there, and then copying them over.

Rating: 1 Votes

DeltaMac

13 weeks ago

Too Bad we can't download older versions of macOS on the App Store now.

Rating: 1 Votes

Tech198

7 weeks ago

Phew.. ! I thought i was going nuts.... I was blaming VMWare fusion for this exact error, which forced me to download a fresh copy every few weeks... of Mojave mostly.

I was wondering why an installer, which worked after downloading, "didn't" work when i came to install again a few "days" later, or so when its just sitting on an external USB drive doing nothing..

Expired certificate in installer huh ? Well, lets hope it's fixed..

Now i'm know i know i'm not crazy, i can sleep better.. :)

Too Bad we can't download older versions of macOS on the App Store now.

Not related, but i got round this by installing Yosemite in VM, then using that to login to App store and download all past OS's :)

Apple's not gonna stop me...

Rating: 1 Votes

McLover66

13 weeks ago

This might be a stupid question, but I have noticed the installers are .dmg files and not .app files like when they come from the App Store. How do I make a bootable installer with terminal now? Could someone please explain this to me? That would help me out a great deal.

Rating: 1 Votes

bsbeamer

13 weeks ago

So at what point can we assume Apple has updated the certificate on those installers and redownload?

# ProductID Version Build Post Date Title
1 061-36794 10.15 19A603 2019-10-21 macOS Catalina
2 041-91758 10.13.6 17G66 2019-10-19 macOS High Sierra
3 041-88800 10.14.4 18E2034 2019-10-23 macOS Mojave
4 061-26589 10.14.6 18G103 2019-10-14 macOS Mojave
5 041-90855 10.13.5 17F66a 2019-10-23 Install macOS High Sierra Beta
6 061-26578 10.14.5 18F2059 2019-10-14 macOS Mojave

Rating: 1 Votes

tywebb13

12 weeks ago

Another weird problem I'm having is the error: ''..... is not a valid mount point'' in terminal. It only happens when I want to make a Sierra bootable installer, all the others work fine. Changing the name of the USB drive does not solve the issue and I've checked the path and it's correct. Does anyone else has this issue with the new 10.12 Sierra installer?

Indeed. I was so curious about your post that I downloaded Sierra and attempted to make the bootable usb to see if this bug is reproducible.

I got the same result.

The reproducibility of the bug makes it very suitable to apple for a bug report.

I have submitted the bug report to apple.

Rating: 1 Votes

Xenomorph

13 weeks ago

I cannot download macOS Catalina right now.

macOS Catalina, 10.15:

[URL unfurl="true"]https://apps.apple.com/us/app/macos-catalina/id1466841314?mt=12[/URL]

"The requested version of macOS is not available."

Rating: 1 Votes

bsbeamer

13 weeks ago

For those having issues downloading, you may want to look into the "installinstallmacos.py" script.

Rating: 1 Votes

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