Font can't be installed: "the font file is corrupt" or "not a valid font file"
Last reviewed 2026-09-19
A font is a set of tables, each with a checksum, plus a checksum for the whole file. Windows, Font Book, print shops and some apps reject a font when any of that is wrong, even though the letter shapes inside are fine.
Messages you might see
- “The font file could not be installed because it is corrupt.”
- “This is not a valid font file.”
- “Validation failed / The font is damaged (Font Book)”
Why it happens
- The font was cut off or modified by a download or a conversion tool.
- A font editor saved wrong checksums or a badly ordered table directory.
- The file is actually a WOFF web font or a font collection (.ttc) with the wrong extension.
Try this first (free, no tool needed)
- Download the font again from the original source.
- Check that it is a .ttf or .otf, not .woff, .woff2 or a .ttc collection.
- On a Mac, use Font Book's Validate Font to see what it complains about.
- Open it in a font editor such as FontForge and generate a fresh copy.
If that didn't work
These tools run in your browser. Your file is read and repaired on your own device and is never uploaded.
Corrupted Font File Repair
Rebuilds the table directory and every table checksum, corrects the whole-file checksum, the glyph-index format flag and glyph positions that run past the end of the outline data, and adds a minimal name / post table if missing. It fixes the structure around the glyphs; it cannot recreate outlines that are gone and does not convert WOFF or split collections.
Open Corrupted Font File RepairCommon questions
Does it change how the font looks?
No. Glyph outlines are carried over unchanged. Only the surrounding structure and checksums are rewritten.
Is my file uploaded anywhere?
No. The tool runs as a program inside your own browser, so the file is read and repaired on your device and never sent to a server.