# EPUBCheck RSC-028: XML documents must be encoded in UTF-8…

Source: https://epublab.com/epubcheck/rsc-028/ (updated 2026-11-03)

EPUBCheck RSC-028 is an error message: “XML documents must be encoded in UTF-8, but … was detected.” An XML file uses an encoding other than UTF-8, which EPUB requires for XML documents.

- Official message (EPUBCheck 5.4.0): XML documents must be encoded in UTF-8, but %1$s was detected.
- Default severity: Error

## Typical causes

- A file saved as ISO-8859-1, Windows-1252 or another legacy encoding, often declared in its XML declaration.

## How to fix it

- Convert the file to UTF-8 and change the XML declaration to encoding="UTF-8" (or remove the encoding attribute).

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