# EPUBCheck OPF-045: circular fallback chain, how to fix it

Source: https://epubcc.com/epubcheck/opf-045/ (updated 2026-11-04)

EPUBCheck OPF-045 is an error message: “Encountered circular reference in fallback chain.” A manifest fallback chain is circular: following the fallback attributes leads back to an item already in the chain. A reading app looking for a format it can render would loop forever.

- Official message (EPUBCheck 5.4.0): Encountered circular reference in fallback chain.
- Default severity: Error

## Typical causes

- Two items that name each other as fallback.
- A longer chain whose last item points back to the first.
- Fallbacks edited by hand without checking the whole chain.

## How to fix it

1. Start at the item EPUBCheck points to and write down each fallback in turn.
2. Remove the fallback attribute from the item that points back into the chain.
3. Make sure the chain ends at a content document (for spine items) or a core media type.

## When it's not this

If a fallback points to an id that does not exist, that is OPF-040.

## 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.