# OPF-013: declared media types differ, how to fix it

Source: https://epubcc.com/epubcheck/opf-013/ (updated 2026-11-04)

EPUBCheck OPF-013 is a warning message: “Resource "…" is declared with MIME type "…" in content, but has MIME type "…" in the package document.” A content document declares one media type for a resource and the manifest declares another. Reading apps may trust either value, so a mismatch can stop the resource from playing or displaying.

- Official message (EPUBCheck 5.4.0): Resource "%1$s" is declared with MIME type "%2$s" in content, but has MIME type "%3$s" in the package document.
- Default severity: Warning

## Typical causes

- An object, embed, link or source element whose type attribute disagrees with the manifest item.
- A file converted to another format (for example, audio re-encoded) without updating every declaration.
- A type attribute copied from a web page that used a different format.

## How to fix it

1. Check the real format of the file EPUBCheck names.
2. Set the manifest media-type to that real format.
3. Make the type attribute in the content document say the same, or remove the type attribute if the element does not need it.

## When it's not this

If the file's content does not match the manifest media type, that is OPF-029.

## Sources

- EPUB 3.3, §5.6.2 The item element: https://www.w3.org/TR/epub-33/#sec-item-elem (read 2026-11-04)

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