# OPF-012: property wrong for file type, how to fix it

Source: https://epubcc.com/epubcheck/opf-012/ (updated 2026-11-04)

EPUBCheck OPF-012 is an error message: “Item property "…" is not defined for media type "…".” A manifest item has a property that does not apply to its media type. Manifest properties describe what a file is or contains, and each one is only defined for certain kinds of file.

- Official message (EPUBCheck 5.4.0): Item property "%1$s" is not defined for media type "%2$s".
- Default severity: Error

## Typical causes

- cover-image on a file that is not an image, such as the XHTML page that shows the cover.
- nav on a file that is not an XHTML document.
- svg, mathml or scripted on a file that is not a content document, such as a stylesheet or an image.

## How to fix it

1. Read the property and media type EPUBCheck names in the message.
2. Move the property to the item it really describes, for example cover-image to the image file itself.
3. Remove the property if no item should carry it, then run EPUBCheck again.

## When it's not this

If the property simply does not exist in the vocabulary, that is OPF-027.

## Sources

- EPUB 3.3, §5.6.2.1 Resource properties: https://www.w3.org/TR/epub-33/#sec-item-resource-properties (read 2026-11-04)

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