# EPUBCheck OPF-005: Invalid prefix declaration: URI for…

Source: https://epublab.com/epubcheck/opf-005/ (updated 2026-11-03)

EPUBCheck OPF-005 is an error message: “Invalid prefix declaration: URI for prefix "…" doesn’t exist.” A prefix in the prefix attribute has no URI after it.

- Official message (EPUBCheck 5.4.0): Invalid prefix declaration: URI for prefix "%1$s" doesn’t exist.
- Default severity: Error

## Typical causes

- A mapping cut short, such as "ibooks:" at the end of the attribute.
- Hand-edited or tool-generated package documents that write the prefix attribute with the wrong separators.

## How to fix it

- The prefix attribute on the package element maps short prefixes to vocabulary URIs, as space-separated pairs like prefix="ibooks: http://vocabulary.itunes.apple.com/rdf/ibooks/vocabulary-extensions-1.0/". Add the vocabulary URI after the prefix, or remove the prefix.
- Reserved prefixes such as dcterms, rendition and schema need no declaration at all.

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