# RSC-032: foreign resource, no fallback, how to fix it

Source: https://epubcc.com/epubcheck/rsc-032/ (updated 2026-11-04)

EPUBCheck RSC-032 is an error message: “Fallback must be provided for foreign resources, but found none for resource "…" of type "…".” A resource in a format reading apps are not required to support (a foreign resource) is used without a fallback in a core format. Without a fallback, apps that cannot display it show nothing.

- Official message (EPUBCheck 5.4.0): Fallback must be provided for foreign resources, but found none for resource "%1$s" of type "%2$s".
- Default severity: Error

## Typical causes

- Images in TIFF, BMP or another non-core format referenced directly from the content.
- Embedded objects or media in formats outside the core media types list.

## How to fix it

1. Convert the resource to a core media type (for images: JPEG, PNG, GIF, WebP or SVG).
2. Or provide a fallback: a manifest fallback attribute, or a picture or object element with an alternative.
3. Update the manifest media type and validate again.

## When it's not this

An img pointing at a non-core image format can also be reported as MED-003.

## Sources

- EPUB 3.3, §3.2 Core media types: https://www.w3.org/TR/epub-33/#sec-core-media-types (read 2026-11-04)
- EPUB 3.3, §3.5 Resource fallbacks: https://www.w3.org/TR/epub-33/#sec-resource-fallbacks (read 2026-11-04)

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