# EPUBCheck HTM_057: Viewport … value must be a positive…

Source: https://epublab.com/epubcheck/htm_057/ (updated 2026-11-03)

EPUBCheck HTM_057 is an error message: “Viewport "…" value must be a positive number or the keyword "device-…".” A viewport width or height is not a positive number or the device-width/device-height keyword.

- Official message (EPUBCheck 5.4.0): Viewport "%1$s" value must be a positive number or the keyword "device-%1$s"
- Default severity: Error

## Typical causes

- Values with units (px, %), zero or negative numbers, or typos.

## How to fix it

- Use a plain positive number, for example width=1200.

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