diff --git a/packages/next/server/web/spec-extension/cookies.ts b/packages/next/server/web/spec-extension/cookies.ts
index f6cf48029a7bd..c040b8c5ee08d 100644
--- a/packages/next/server/web/spec-extension/cookies.ts
+++ b/packages/next/server/web/spec-extension/cookies.ts
@@ -37,8 +37,11 @@ const serializeCookie = (input: string[]) => input.join(', ')
 
 export class Cookies extends Map<string, any> {
   constructor(input?: string | null) {
+    super()
     const parsedInput = typeof input === 'string' ? cookie.parse(input) : {}
-    super(Object.entries(parsedInput))
+    for (const [key, value] of Object.entries(parsedInput)) {
+      super.set(key, value)
+    }
   }
   set(key: string, value: unknown, options: CookieSerializeOptions = {}) {
     return super.set(