diff --git a/lib/util/cache.js b/lib/util/cache.js
index 2ea4cb26b20..d51c202765e 100644
--- a/lib/util/cache.js
+++ b/lib/util/cache.js
@@ -13,6 +13,24 @@ function makeCacheKey (opts) {
     throw new Error('opts.origin is undefined')
   }
 
+  /** @type {Record<string, string[] | string>} */
+  let headers
+  if (opts.headers == null) {
+    headers = {}
+  } else if (typeof opts.headers[Symbol.iterator] === 'function') {
+    headers = {}
+    for (const [key, val] of opts.headers) {
+      if (typeof key !== 'string' || typeof val !== 'string') {
+        throw new Error('opts.headers is not a valid header map')
+      }
+      headers[key] = val
+    }
+  } else if (typeof opts.headers === 'object') {
+    headers = opts.headers
+  } else {
+    throw new Error('opts.headers is not an object')
+  }
+
   /**
    * @type {import('../../types/cache-interceptor.d.ts').default.CacheKey}
    */
@@ -20,7 +38,7 @@ function makeCacheKey (opts) {
     origin: opts.origin.toString(),
     method: opts.method,
     path: opts.path,
-    headers: opts.headers
+    headers
   }
 
   return cacheKey
diff --git a/types/dispatcher.d.ts b/types/dispatcher.d.ts
index 8b9e633d730..069fed63ac4 100644
--- a/types/dispatcher.d.ts
+++ b/types/dispatcher.d.ts
@@ -103,7 +103,7 @@ declare namespace Dispatcher {
     /** Default: `null` */
     body?: string | Buffer | Uint8Array | Readable | null | FormData;
     /** Default: `null` */
-    headers?: IncomingHttpHeaders | string[] | Iterable<[string, string | string[] | undefined]> | null;
+    headers?: Record<string, string | string[]> | IncomingHttpHeaders | string[] | Iterable<[string, string | string[] | undefined]> | null;
     /** 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`. */