# EPUBCheck PKG-010: The file name … contains spaces, which…

Source: https://epublab.com/epubcheck/pkg-010/ (updated 2026-11-03)

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, which is allowed but can break older reading systems.

- 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".

## How to fix it

- Rename the file with hyphens or underscores instead of spaces.
- 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.
- If you keep the space, every URL that points to the file must encode it as %20.

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