Fix MSSIPOTF_E_PCONST_CHECK 0x80097017 Font Error on Windows

Your PC can't open a font because a table check failed. Usually a corrupted font file or a bad app update. Quick fix: reinstall the font or roll back the last change.

Quick answer for pros: Delete the corrupted font file from C:\Windows\Fonts or C:\Users\[YourName]\AppData\Local\Microsoft\Windows\Fonts, then reinstall it from the original source. If that doesn't work, run sfc /scannow and DISM /Online /Cleanup-Image /RestoreHealth from an admin command prompt.

What's actually happening here

This error shows up when Windows tries to load a font file and the signature check fails on a partially constant table — think of it like a PDF with a broken internal index. The font file is either corrupted on disk, got mangled during an app update, or was downloaded from a sketchy site. I've seen it most often after a Windows Update drops a new font version that conflicts with an older one, or when someone copies a font from a Mac without properly converting it. A client last month got this after a Chrome update borked the Google Fonts cache — took me 10 minutes to figure out.

Fix steps (in order, don't skip around)

Find the bad font. The error message usually names the font file. If not, check the Event Viewer (Windows Logs > System) for the font name. Most common culprits: segoeui.ttf, arial.ttf, or any custom font you recently installed.
Delete that font. Open File Explorer, go to C:\Windows\Fonts, search for the font file. Right-click and delete. If it says 'in use', close all apps — especially browsers and Office — and try again. Use Unlocker or a bootable USB if it's really stuck.
Reinstall the font from a clean source. Download the font from the original vendor or a trusted site like fonts.google.com. Right-click the new .ttf or .otf file, choose 'Install'. Restart the app that showed the error.
Run system file checker. Open Command Prompt as admin, type sfc /scannow, let it finish. If it finds corrupted files, run DISM /Online /Cleanup-Image /RestoreHealth right after.
Roll back any recent updates. If the error started after a Windows Update, go to Settings > Update & Security > View update history > Uninstall updates. Remove the latest update, reboot.

When the main fix doesn't work

Sometimes the problem isn't a single font — it's a corrupted font cache. Here's the alternative:

Close all apps. Open Services (type services.msc in Run), stop 'Windows Font Cache Service'. Delete the folder C:\Windows\ServiceProfiles\LocalService\AppData\Local\FontCache. Restart the service.
If the error appears in a specific app (like Photoshop or Word), reinstall the app completely. I had a case where a bad Office add-in was replacing fonts.
As a last resort, do a system restore to a point before the error started. Type rstrui in Run, pick a restore point, and let it roll back.

How to keep it from coming back

Don't download fonts from random font websites — stick to Google Fonts or Adobe Fonts. When you install a new app, watch for font conflicts — some apps dump custom fonts into the system folder. Also, run sfc /scannow once a month if you're prone to crashes. And for the love of tech, never delete a system font like Segoe UI unless you're ready to reinstall Windows.

Pro tip: If you're a designer, keep your personal fonts in C:\Users\[YourName]\AppData\Local\Microsoft\Windows\Fonts instead of the system folder. That way, a bad font won't hose your entire OS.

That's it. 20 minutes of work, tops. Go grab a coffee after.