# EPUBCheck HTM-009: obsolete DOCTYPE to remove, how to fix it

Source: https://epubcc.com/epubcheck/htm-009/ (updated 2026-11-04)

EPUBCheck HTM-009 is an error message: “The DOCTYPE provided is obsolete or irregular and can be removed.” A document's DOCTYPE is obsolete or irregular and can simply be removed. EPUB only allows a few external identifiers in DOCTYPEs (for MathML, the NCX and SVG 1.1); anything else is reported.

- Official message (EPUBCheck 5.4.0): The DOCTYPE provided is obsolete or irregular and can be removed.
- Default severity: Error

## Typical causes

- Old DOCTYPEs kept from earlier versions of the book, such as XHTML 1.1 or HTML 4 identifiers.
- A DOCTYPE added by an editor or converter that uses a web template for every file.

## 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. Remove the DOCTYPE line, or replace it with <!DOCTYPE html> in XHTML content documents.
3. Check that the file still has its XML declaration and the html element with the XHTML namespace xmlns="http://www.w3.org/1999/xhtml".
4. Rebuild the EPUB and run EPUBCheck again to confirm the message is gone.

## When it's not this

If EPUBCheck tells you which DOCTYPE it expected instead, the message is HTM-004.

## Sources

- EPUB 3.3, §B. Allowed external identifiers: https://www.w3.org/TR/epub-33/#app-identifiers-allowed (read 2026-11-04)

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