diff --git a/src/utils.ts b/src/utils.ts
index 70003ad26..665768d98 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -711,6 +711,9 @@ export const unsignCookie = async (input: string, secret: string | null) => {
 	}
 
 	const tentativeValue = input.slice(0, dot)
+
+	if (secret === null) return false
+
 	const expectedInput = await signCookie(tentativeValue, secret)
 
 	return constantTimeEqual(expectedInput, input) ? tentativeValue : false
diff --git a/test/cookie/signature.test.ts b/test/cookie/signature.test.ts
index 0eb5a8800..2a15025f0 100644
--- a/test/cookie/signature.test.ts
+++ b/test/cookie/signature.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, it } from 'bun:test'
 import { parseCookie, Cookie } from '../../src/cookies'
 import { signCookie } from '../../src/utils'
+import { InvalidCookieSignature } from '../../src/error'
 
 describe('Parse Cookie', () => {
 	it('handle empty cookie', async () => {
@@ -134,4 +135,19 @@ describe('Parse Cookie', () => {
 
 		expect(result.fischl.value).toEqual('fischl')
 	})
+
+	it('rejects invalid signature with null secret in rotation', async () => {
+		const set = {
+			headers: {},
+			cookie: {}
+		}
+
+		const cookieString = `wizard=1.invalid_sign`
+		await expect(
+			parseCookie(set, cookieString, {
+				secrets: ['valid-secret', null],
+				sign: ['wizard']
+			})
+		).rejects.toThrow(InvalidCookieSignature)
+	})
 })