diff --git a/docs/docs/api/Dispatcher.md b/docs/docs/api/Dispatcher.md
index d9f66d17d81..ec0565316ab 100644
--- a/docs/docs/api/Dispatcher.md
+++ b/docs/docs/api/Dispatcher.md
@@ -194,7 +194,7 @@ Returns: `Boolean` - `false` if dispatcher is busy and further dispatch calls wo
 * **method** `string`
 * **reset** `boolean` (optional) - Default: `false` - If `false`, the request will attempt to create a long-living connection by sending the `connection: keep-alive` header,otherwise will attempt to close it immediately after response by sending `connection: close` within the request and closing the socket afterwards.
 * **body** `string | Buffer | Uint8Array | stream.Readable | Iterable | AsyncIterable | null` (optional) - Default: `null`
-* **headers** `UndiciHeaders | string[]` (optional) - Default: `null`.
+* **headers** `UndiciHeaders` (optional) - Default: `null`.
 * **query** `Record<string, any> | null` (optional) - Default: `null` - Query string params to be embedded in the request URL. Note that both keys and values of query are encoded using `encodeURIComponent`. If for some reason you need to send them unencoded, embed query params into path directly instead.
 * **idempotent** `boolean` (optional) - Default: `true` if `method` is `'HEAD'` or `'GET'` - Whether the requests can be safely retried or not. If `false` the request won't be sent until all preceding requests in the pipeline has completed.
 * **blocking** `boolean` (optional) - Default: `method !== 'HEAD'` - Whether the response is expected to take a long time and would end up blocking the pipeline. When this is set to `true` further pipelining will be avoided on the same connection until headers have been received.
diff --git a/test/types/dispatcher.test-d.ts b/test/types/dispatcher.test-d.ts
index 77f5320c1c4..4f26dc0adf1 100644
--- a/test/types/dispatcher.test-d.ts
+++ b/test/types/dispatcher.test-d.ts
@@ -22,15 +22,23 @@ expectAssignable<Dispatcher>(new Dispatcher())
       yield ['hello', 'world']
     }
   }
+  const recordHeadersString: Record<string, string> = { hello: 'world' }
+  const recordHeadersStringArray: Record<string, string[]> = { foo: ['hello', 'world'] }
+  const recordHeadersUndefined: Record<string, undefined> = { bar: undefined }
 
   // dispatch
   expectAssignable<boolean>(dispatcher.dispatch({ path: '', method: 'GET' }, {}))
   expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET' }, {}))
   expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: { authorization: undefined } }, {}))
   expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: [] }, {}))
+  expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: ['hello', 'world'] }, {}))
   expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: {} }, {}))
   expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: nodeCoreHeaders }, {}))
   expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: null, reset: true }, {}))
+  expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: undefined, reset: true }, {}))
+  expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: recordHeadersString, reset: true }, {}))
+  expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: recordHeadersStringArray, reset: true }, {}))
+  expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: recordHeadersUndefined, reset: true }, {}))
   expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: headerInstanceHeaders, reset: true }, {}))
   expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: mapHeaders, reset: true }, {}))
   expectAssignable<boolean>(dispatcher.dispatch({ origin: '', path: '', method: 'GET', headers: iteratorHeaders, reset: true }, {}))
@@ -50,6 +58,19 @@ expectAssignable<Dispatcher>(new Dispatcher())
   }))
   expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', responseHeaders: 'raw' }))
   expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', responseHeaders: null }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: { authorization: undefined } }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: [] }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: ['hello', 'world'] }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: {} }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: nodeCoreHeaders }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: null }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: undefined }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: recordHeadersString }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: recordHeadersStringArray }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: recordHeadersUndefined }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: headerInstanceHeaders }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: mapHeaders }))
+  expectAssignable<Promise<Dispatcher.ConnectData>>(dispatcher.connect({ origin: '', path: '', headers: iteratorHeaders }))
 
   // request
   expectAssignable<Promise<Dispatcher.ResponseData>>(dispatcher.request({ origin: '', path: '', method: 'GET', maxRedirections: 0 }))
@@ -156,6 +177,19 @@ expectAssignable<Dispatcher>(new Dispatcher())
   }))
   expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', responseHeaders: 'raw' }))
   expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', responseHeaders: null }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: { authorization: undefined } }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: [] }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: ['hello', 'world'] }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: {} }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: nodeCoreHeaders }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: null }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: undefined }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: recordHeadersString }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: recordHeadersStringArray }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: recordHeadersUndefined }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: headerInstanceHeaders }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: mapHeaders }))
+  expectAssignable<Promise<Dispatcher.UpgradeData>>(dispatcher.upgrade({ path: '', method: 'GET', headers: iteratorHeaders }))
 
   // close
   expectAssignable<Promise<void>>(dispatcher.close())
diff --git a/types/dispatcher.d.ts b/types/dispatcher.d.ts
index 17bb44166fa..0584e36f565 100644
--- a/types/dispatcher.d.ts
+++ b/types/dispatcher.d.ts
@@ -12,6 +12,8 @@ type AbortSignal = unknown
 
 export default Dispatcher
 
+export type UndiciHeaders = Record<string, string | string[]> | IncomingHttpHeaders | string[] | Iterable<[string, string | string[] | undefined]> | null
+
 /** Dispatcher is the core API used to dispatch requests. */
 declare class Dispatcher extends EventEmitter {
   /** Dispatches a request. This API is expected to evolve through semver-major versions and is less stable than the preceding higher level APIs. It is primarily intended for library developers who implement higher level APIs on top of this. */
@@ -103,7 +105,7 @@ declare namespace Dispatcher {
     /** Default: `null` */
     body?: string | Buffer | Uint8Array | Readable | null | FormData;
     /** Default: `null` */
-    headers?: Record<string, string | string[]> | IncomingHttpHeaders | string[] | Iterable<[string, string | string[] | undefined]> | null;
+    headers?: UndiciHeaders;
     /** Query string params to be embedded in the request URL. Default: `null` */
     query?: Record<string, any>;
     /** Whether the requests can be safely retried or not. If `false` the request won't be sent until all preceding requests in the pipeline have completed. Default: `true` if `method` is `HEAD` or `GET`. */
@@ -127,7 +129,7 @@ declare namespace Dispatcher {
     origin: string | URL;
     path: string;
     /** Default: `null` */
-    headers?: IncomingHttpHeaders | string[] | null;
+    headers?: UndiciHeaders;
     /** Default: `null` */
     signal?: AbortSignal | EventEmitter | null;
     /** This argument parameter is passed through to `ConnectData` */
@@ -164,7 +166,7 @@ declare namespace Dispatcher {
     /** Default: `'GET'` */
     method?: string;
     /** Default: `null` */
-    headers?: IncomingHttpHeaders | string[] | null;
+    headers?: UndiciHeaders;
     /** A string of comma separated protocols, in descending preference order. Default: `'Websocket'` */
     protocol?: string;
     /** Default: `null` */