# EPUBCheck HTM-001: XML version is not 1.0, how to fix it

Source: https://epubcc.com/epubcheck/htm-001/ (updated 2026-11-04)

EPUBCheck HTM-001 is an error message: “Any publication resource that is an XML-based media type must be a valid XML 1.0 document. XML version found: ….” An XML file in the EPUB declares an XML version other than 1.0. EPUB requires every XML-based resource (XHTML chapters, the package document, the NCX, SVG images) to be a valid XML 1.0 document, and EPUBCheck names the version it found.

- Official message (EPUBCheck 5.4.0): Any publication resource that is an XML-based media type must be a valid XML 1.0 document. XML version found: %1$s.
- Default severity: Error

## Typical causes

- An XML declaration that says version="1.1", written by an editor or an export tool that defaults to it.
- A template copied from another XML project and reused for every chapter.

## How to fix it

1. Open the file EPUBCheck names (the message gives the path, line and column) in a text or EPUB editor such as Sigil, or unzip the EPUB and open it there.
2. Change the first line to <?xml version="1.0" encoding="UTF-8"?>, or remove the XML declaration: without one, XML 1.0 and UTF-8 are assumed.
3. If the tool that made the book writes 1.1 in every file, fix its template so the next export is right.
4. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

## When it's not this

If the declaration says 1.0 but the file is saved in UTF-16, that is HTM_058, not HTM-001.

## Sources

- EPUB 3.3, §3.9 XML conformance: https://www.w3.org/TR/epub-33/#sec-xml-constraints (read 2026-11-04)

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