# EPUBCheck OPF-001: unreadable EPUB version, how to fix it

Source: https://epubcc.com/epubcheck/opf-001/ (updated 2026-11-04)

EPUBCheck OPF-001 is an error message: “There was an error when parsing the EPUB version: ….” EPUBCheck could not read the EPUB version from the package document. The version attribute on the package element tells validators and reading apps which set of rules the book follows, so without a readable value the rest of the check is unreliable.

- Official message (EPUBCheck 5.4.0): There was an error when parsing the EPUB version: %1$s.
- Default severity: Error

## Typical causes

- A missing or empty version attribute on the package element.
- A malformed value, such as version="3" or version="EPUB 3", instead of a number like 3.0.
- A package element written by hand or by a script that left the attribute out.

## How to fix it

1. Open the package document (the .opf file) and find the package element at the top.
2. Set version="3.0" for EPUB 3 (EPUB 3.3 books still declare 3.0) or version="2.0" for EPUB 2.
3. Run EPUBCheck again: errors that depended on the version should now be reported correctly.

## When it's not this

If EPUBCheck reads the version but you asked for a different one with -v, that is PKG-001, not OPF-001.

## Sources

- EPUB 3.3, §5.4 The package element: https://www.w3.org/TR/epub-33/#sec-package-elem (read 2026-11-04)

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EpubCC.