diff --git a/.changeset/dry-hornets-change.md b/.changeset/dry-hornets-change.md
new file mode 100644
index 000000000000..12d873587ebf
--- /dev/null
+++ b/.changeset/dry-hornets-change.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-node': minor
+---
+
+validate ORIGIN env var at startup
diff --git a/packages/adapter-node/src/handler.js b/packages/adapter-node/src/handler.js
index b1a40bb19955..fd25fddf50c2 100644
--- a/packages/adapter-node/src/handler.js
+++ b/packages/adapter-node/src/handler.js
@@ -9,13 +9,22 @@ import { getRequest, setResponse, createReadableStream } from '@sveltejs/kit/nod
 import { Server } from 'SERVER';
 import { manifest, prerendered, base } from 'MANIFEST';
 import { env } from 'ENV';
-import { parse_as_bytes } from '../utils.js';
+import { parse_as_bytes, parse_origin } from '../utils.js';
 
 /* global ENV_PREFIX */
 
 const server = new Server(manifest);
 
-const origin = env('ORIGIN', undefined);
+const origin = parse_origin(env('ORIGIN', undefined));
+
+if (origin === undefined && env('ORIGIN', undefined) !== undefined) {
+	throw new Error(
+		`Invalid ORIGIN: '${env('ORIGIN', undefined)}'. ` +
+			`ORIGIN must be a valid URL with http:// or https:// protocol. ` +
+			`For example: 'http://localhost:3000' or 'https://my.site'`
+	);
+}
+
 const xff_depth = parseInt(env('XFF_DEPTH', '1'));
 const address_header = env('ADDRESS_HEADER', '').toLowerCase();
 const protocol_header = env('PROTOCOL_HEADER', '').toLowerCase();
diff --git a/packages/adapter-node/tests/utils.spec.js b/packages/adapter-node/tests/utils.spec.js
index 06a495fde9ba..0ffccd315e62 100644
--- a/packages/adapter-node/tests/utils.spec.js
+++ b/packages/adapter-node/tests/utils.spec.js
@@ -1,5 +1,5 @@
 import { expect, test, describe } from 'vitest';
-import { parse_as_bytes } from '../utils.js';
+import { parse_as_bytes, parse_origin } from '../utils.js';
 
 describe('parse_as_bytes', () => {
 	test('parses correctly', () => {
@@ -19,3 +19,47 @@ describe('parse_as_bytes', () => {
 		});
 	});
 });
+
+describe('parse_origin', () => {
+	test('valid origins return normalized origin', () => {
+		const testCases = [
+			{ input: 'http://localhost:3000', expected: 'http://localhost:3000' },
+			{ input: 'https://example.com', expected: 'https://example.com' },
+			{ input: 'http://192.168.1.1:8080', expected: 'http://192.168.1.1:8080' },
+			{ input: 'https://my-site.com', expected: 'https://my-site.com' },
+			{ input: 'http://localhost', expected: 'http://localhost' },
+			{ input: 'https://example.com:443', expected: 'https://example.com' },
+			{ input: 'http://example.com:80', expected: 'http://example.com' },
+			{ input: undefined, expected: undefined }
+		];
+
+		testCases.forEach(({ input, expected }) => {
+			const actual = parse_origin(input);
+			expect(actual, `Testing input '${input}'`).toBe(expected);
+		});
+	});
+
+	test('URLs with path/query/hash are normalized to origin', () => {
+		const testCases = [
+			{ input: 'http://localhost:3000/path', expected: 'http://localhost:3000' },
+			{ input: 'http://localhost:3000?query=1', expected: 'http://localhost:3000' },
+			{ input: 'http://localhost:3000#hash', expected: 'http://localhost:3000' },
+			{ input: 'https://example.com/path/to/page', expected: 'https://example.com' },
+			{ input: 'https://example.com:443/path?query=1#hash', expected: 'https://example.com' }
+		];
+
+		testCases.forEach(({ input, expected }) => {
+			const actual = parse_origin(input);
+			expect(actual, `Testing input '${input}'`).toBe(expected);
+		});
+	});
+
+	test('invalid origins return undefined', () => {
+		const invalidInputs = ['localhost:3000', 'example.com', '', '   ', 'ftp://localhost:3000'];
+
+		invalidInputs.forEach((input) => {
+			const actual = parse_origin(input);
+			expect(actual, `Testing input '${input}'`).toBeUndefined();
+		});
+	});
+});
diff --git a/packages/adapter-node/utils.js b/packages/adapter-node/utils.js
index 16769eaa0027..234f6a7e888f 100644
--- a/packages/adapter-node/utils.js
+++ b/packages/adapter-node/utils.js
@@ -13,3 +13,34 @@ export function parse_as_bytes(value) {
 		}[value[value.length - 1]?.toUpperCase()] ?? 1;
 	return Number(multiplier != 1 ? value.substring(0, value.length - 1) : value) * multiplier;
 }
+
+/**
+ * Parses and validates an origin URL.
+ *
+ * @param {string | undefined} value - Origin URL with http:// or https:// protocol
+ * @returns {string | undefined} The validated origin, or undefined if value is undefined
+ */
+export function parse_origin(value) {
+	if (value === undefined) {
+		return undefined;
+	}
+
+	const trimmed = value.trim();
+
+	if (trimmed === '') {
+		return undefined;
+	}
+
+	try {
+		const url = new URL(trimmed);
+
+		// Verify protocol is http or https
+		if (url.protocol !== 'http:' && url.protocol !== 'https:') {
+			return undefined;
+		}
+
+		return url.origin;
+	} catch {
+		return undefined;
+	}
+}