sveltejs/kit · error · Error

You should change envPrefix (${env_prefix}) to avoid conflic

Error message

You should change envPrefix (${env_prefix}) to avoid conflicts with existing environment variables — unexpectedly saw ${name}

What it means

adapter-bun lets you set an env_prefix so only variables with that prefix are exposed to the app. At startup it scans process.env and throws if a prefixed variable exists that is not one of the recognized special variables (like PORT_HEADER). This guards against accidentally leaking or misnaming environment variables that would shadow existing ones.

Source

Thrown at packages/adapter-bun/src/env.js:24

	'HOST',
	'PORT',
	'REUSE_PORT',
	'IPV6_ONLY',
	'CONNECTION_IDLE_TIMEOUT',
	'BODY_SIZE_LIMIT',
	'SHUTDOWN_TIMEOUT',
	'DEVELOPMENT',
	'XFF_DEPTH',
	'ADDRESS_HEADER',
	'PROTOCOL_HEADER',
	'HOST_HEADER',
	'PORT_HEADER'
]);

if (env_prefix) {
	for (const name in process.env) {
		if (name.startsWith(env_prefix) && !expected.has(name.slice(env_prefix.length))) {
			throw new Error(
				`You should change envPrefix (${env_prefix}) to avoid conflicts with existing environment variables — unexpectedly saw ${name}`
			);
		}
	}
}

/**
 * @param {string} name
 * @param {string} value
 * @param {string} expected
 * @returns {never}
 */
function parsing_error(name, value, expected) {
	throw new Error(
		`Invalid value for environment variable ${env_prefix + name}: ${JSON.stringify(value)} (expected ${expected})`
	);
}

View on GitHub (pinned to 03f1687fe6)

Solutions

1. Change the envPrefix adapter option to a more unique prefix (e.g. 'MYAPP_') so it no longer matches unrelated variables.
2. Remove or rename the offending environment variable from your deployment environment.
3. If the variable is legitimate, load it through env() so its name is in the expected set.

Example fix

// before
adapterBun({ envPrefix: 'PUBLIC_' }); // PUBLIC_URL exists in env
// after
adapterBun({ envPrefix: 'MYSITE_PUBLIC_' });

const prefix = 'MYSITE_PUBLIC_';
const unexpected = Object.keys(process.env).filter(
  (k) => k.startsWith(prefix) && !['URL'].includes(k.slice(prefix.length))
);
if (unexpected.length) throw new Error(`Colliding env vars: ${unexpected.join(', ')}`);

When it happens

Trigger: Setting env_prefix to a prefix that matches variables already present in the deployment environment (e.g. envPrefix='PUBLIC_' with PUBLIC_URL set) when the variable is not consumed via env() with an expected name.

Common situations: Choosing a generic prefix like PUBLIC_ or APP_ that collides with host platform or CI environment variables; renaming app code without cleaning up stale prefixed variables left in the environment.

Related errors

• Invalid value for environment variable ${env_prefix + name}:
• You should change envPrefix (${env_prefix}) to avoid conflic
• Invalid value for environment variable ${name}: ${JSON.strin
• Invalid BODY_SIZE_LIMIT: '${env('BODY_SIZE_LIMIT')}'. Please
• Cannot build with ${JSON.stringify(file)} because Bun treats

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/c37edc5e8c870470. Report an issue: GitHub.