# EPUBCheck OPF-040: fallback item not found, how to fix it

Source: https://epubcc.com/epubcheck/opf-040/ (updated 2026-11-04)

EPUBCheck OPF-040 is an error message: “Fallback item with id "…" could not be found.” A manifest item's fallback attribute names an id that no manifest item has. Fallbacks let a reading app switch to another format it can render, so a broken fallback chain can leave content unreadable.

- Official message (EPUBCheck 5.4.0): Fallback item with id "%1$s" could not be found.
- Default severity: Error

## Typical causes

- The fallback item was removed or its id renamed.
- A typo in the fallback attribute.
- A fallback copied from another book's manifest.

## How to fix it

1. Read the id EPUBCheck names.
2. Point the fallback at an existing item id, or add the missing item.
3. Remove the fallback if the resource is a core media type and needs none.

## When it's not this

If the fallback chain loops back on itself, that is OPF-045.

## Sources

- EPUB 3.3, §3.5.1 Manifest fallbacks: https://www.w3.org/TR/epub-33/#sec-manifest-fallbacks (read 2026-11-04)

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