diff --git a/test/types/fetch.test-d.ts b/test/types/fetch.test-d.ts
index 583ad3b8675..8c878e5226b 100644
--- a/test/types/fetch.test-d.ts
+++ b/test/types/fetch.test-d.ts
@@ -60,6 +60,11 @@ expectType<Headers>(new Headers([]))
 expectType<Headers>(new Headers(headers))
 expectType<Headers>(new Headers(undefined))
 
+expectAssignable<HeadersInit>({ 'a': 'b' } as Record<string, string>)
+expectAssignable<HeadersInit>({ 'content-type': 'application/gzip' } satisfies HeadersInit)
+expectAssignable<HeadersInit>({ 'Content-Type': 'nonstandard/mime' } satisfies HeadersInit)
+expectNotAssignable<HeadersInit>([['1', '2', '3']])
+
 expectType<Request>(new Request(request))
 expectType<Request>(new Request('https://example.com'))
 expectType<Request>(new Request(new URL('https://example.com')))
diff --git a/types/fetch.d.ts b/types/fetch.d.ts
index 7e94375ecdc..20c1839acd2 100644
--- a/types/fetch.d.ts
+++ b/types/fetch.d.ts
@@ -6,7 +6,7 @@ import { Blob } from 'buffer'
 import { URL, URLSearchParams } from 'url'
 import { ReadableStream } from 'stream/web'
 import { FormData } from './formdata'
-
+import { HeaderRecord } from './header'
 import Dispatcher from './dispatcher'
 
 export type RequestInfo = string | URL | Request
@@ -67,7 +67,7 @@ export interface SpecIterable<T> {
   [Symbol.iterator](): SpecIterator<T>;
 }
 
-export type HeadersInit = string[][] | Record<string, string | ReadonlyArray<string>> | Headers
+export type HeadersInit = [string, string][] | HeaderRecord | Headers
 
 export declare class Headers implements SpecIterable<[string, string]> {
   constructor (init?: HeadersInit)
diff --git a/types/header.d.ts b/types/header.d.ts
index bfdb3296d4d..355a46ea307 100644
--- a/types/header.d.ts
+++ b/types/header.d.ts
@@ -2,3 +2,155 @@
  * The header type declaration of `undici`.
  */
 export type IncomingHttpHeaders = Record<string, string | string[] | undefined>;
+
+type HeaderNames =
+  | 'Accept'
+  | 'Accept-CH'
+  | 'Accept-Charset'
+  | 'Accept-Encoding'
+  | 'Accept-Language'
+  | 'Accept-Patch'
+  | 'Accept-Post'
+  | 'Accept-Ranges'
+  | 'Access-Control-Allow-Credentials'
+  | 'Access-Control-Allow-Headers'
+  | 'Access-Control-Allow-Methods'
+  | 'Access-Control-Allow-Origin'
+  | 'Access-Control-Expose-Headers'
+  | 'Access-Control-Max-Age'
+  | 'Access-Control-Request-Headers'
+  | 'Access-Control-Request-Method'
+  | 'Age'
+  | 'Allow'
+  | 'Alt-Svc'
+  | 'Alt-Used'
+  | 'Authorization'
+  | 'Cache-Control'
+  | 'Clear-Site-Data'
+  | 'Connection'
+  | 'Content-Disposition'
+  | 'Content-Encoding'
+  | 'Content-Language'
+  | 'Content-Length'
+  | 'Content-Location'
+  | 'Content-Range'
+  | 'Content-Security-Policy'
+  | 'Content-Security-Policy-Report-Only'
+  | 'Content-Type'
+  | 'Cookie'
+  | 'Cross-Origin-Embedder-Policy'
+  | 'Cross-Origin-Opener-Policy'
+  | 'Cross-Origin-Resource-Policy'
+  | 'Date'
+  | 'Device-Memory'
+  | 'ETag'
+  | 'Expect'
+  | 'Expect-CT'
+  | 'Expires'
+  | 'Forwarded'
+  | 'From'
+  | 'Host'
+  | 'If-Match'
+  | 'If-Modified-Since'
+  | 'If-None-Match'
+  | 'If-Range'
+  | 'If-Unmodified-Since'
+  | 'Keep-Alive'
+  | 'Last-Modified'
+  | 'Link'
+  | 'Location'
+  | 'Max-Forwards'
+  | 'Origin'
+  | 'Permissions-Policy'
+  | 'Priority'
+  | 'Proxy-Authenticate'
+  | 'Proxy-Authorization'
+  | 'Range'
+  | 'Referer'
+  | 'Referrer-Policy'
+  | 'Retry-After'
+  | 'Sec-Fetch-Dest'
+  | 'Sec-Fetch-Mode'
+  | 'Sec-Fetch-Site'
+  | 'Sec-Fetch-User'
+  | 'Sec-Purpose'
+  | 'Sec-WebSocket-Accept'
+  | 'Server'
+  | 'Server-Timing'
+  | 'Service-Worker-Navigation-Preload'
+  | 'Set-Cookie'
+  | 'SourceMap'
+  | 'Strict-Transport-Security'
+  | 'TE'
+  | 'Timing-Allow-Origin'
+  | 'Trailer'
+  | 'Transfer-Encoding'
+  | 'Upgrade'
+  | 'Upgrade-Insecure-Requests'
+  | 'User-Agent'
+  | 'Vary'
+  | 'Via'
+  | 'WWW-Authenticate'
+  | 'X-Content-Type-Options'
+  | 'X-Frame-Options'
+  | (string & {})
+
+type KnownHeaderValues = {
+  'content-type':
+    | 'audio/aac'
+    | 'video/x-msvideo'
+    | 'image/avif'
+    | 'video/av1'
+    | 'application/octet-stream'
+    | 'image/bmp'
+    | 'text/css'
+    | 'text/csv'
+    | 'application/vnd.ms-fontobject'
+    | 'application/epub+zip'
+    | 'image/gif'
+    | 'application/gzip'
+    | 'text/html'
+    | 'image/x-icon'
+    | 'text/calendar'
+    | 'image/jpeg'
+    | 'text/javascript'
+    | 'application/json'
+    | 'application/ld+json'
+    | 'audio/x-midi'
+    | 'audio/mpeg'
+    | 'video/mp4'
+    | 'video/mpeg'
+    | 'audio/ogg'
+    | 'video/ogg'
+    | 'application/ogg'
+    | 'audio/opus'
+    | 'font/otf'
+    | 'application/pdf'
+    | 'image/png'
+    | 'application/rtf'
+    | 'image/svg+xml'
+    | 'image/tiff'
+    | 'video/mp2t'
+    | 'font/ttf'
+    | 'text/plain'
+    | 'application/wasm'
+    | 'video/webm'
+    | 'audio/webm'
+    | 'image/webp'
+    | 'font/woff'
+    | 'font/woff2'
+    | 'application/xhtml+xml'
+    | 'application/xml'
+    | 'application/zip'
+    | 'video/3gpp'
+    | 'video/3gpp2'
+    | 'model/gltf+json'
+    | 'model/gltf-binary'
+    | (string & {})
+}
+
+export type HeaderRecord = {
+  [K in HeaderNames | Lowercase<HeaderNames>]?: Lowercase<K> extends keyof KnownHeaderValues
+    ? KnownHeaderValues[Lowercase<K>]
+    : string
+}