# EPUBCheck PKG-010: space in a file name, how to fix it

Source: https://epubcc.com/epubcheck/pkg-010/ (updated 2026-11-04)

EPUBCheck PKG-010 is a warning message: “The file name "…" contains spaces, which may create interoperability issues with older reading systems.” A file name inside the EPUB contains spaces. That is allowed, but it can break older reading systems, and every URL that points to the file then has to encode the space correctly.

- Official message (EPUBCheck 5.4.0): The file name "%1$s" contains spaces, which may create interoperability issues with older reading systems.
- Default severity: Warning

## Typical causes

- Images or chapters named after their original titles, like "Chapter 1.xhtml".
- Files exported from a word processor or layout tool that keeps document names.

## How to fix it

1. Rename the file with hyphens or underscores instead of spaces.
2. After renaming, update every reference to the file: the manifest in the package document, links and image sources in the XHTML, and url() references in the CSS.
3. If you keep the space, every URL that points to the file must encode it as %20.

## When it's not this

If the name has characters such as : or ?, the error is PKG-009; a badly encoded URL is RSC-020.

## Sources

- EPUB 3.3, §4.2.3 File paths and file names: https://www.w3.org/TR/epub-33/#sec-container-filenames (read 2026-11-04)

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