diff --git a/src/index.cts b/src/index.cts
index b76d642..b193d8e 100644
--- a/src/index.cts
+++ b/src/index.cts
@@ -1,3 +1,3 @@
-import factory from "./index.js";
+import factory from "./index.js"
 
-module.exports = factory.default;
+module.exports = factory.default
diff --git a/src/index.ts b/src/index.ts
index 7ab175d..6cb767a 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,7 +1,7 @@
 import { setOptions, setErrorType, setPolyfills } from "./config.js"
 import { core } from "./core.js"
 import { WretchError } from "./resolver.js"
-import type { Wretch } from "./types.js"
+import type { Wretch, WretchOptions } from "./types.js"
 
 export type {
   Wretch,
@@ -33,7 +33,7 @@ export type {
  * @param _options The base fetch options
  * @returns A fresh wretch instance
  */
-function factory(_url = "", _options = {}): Wretch {
+function factory(_url = "", _options: WretchOptions = {}): Wretch {
   return { ...core, _url, _options }
 }
 
diff --git a/src/types.ts b/src/types.ts
index e5914a6..da7fa33 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -761,7 +761,7 @@ export type Config = {
 /**
  * Fetch Request options with additional properties.
  */
-export type WretchOptions = Record<string, any>
+export type WretchOptions = Record<string, any> & RequestInit
 /**
  * An Error enhanced with status, text and body.
  */
diff --git a/src/utils.ts b/src/utils.ts
index ba7b4c8..094e2bc 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -1,7 +1,8 @@
 import { CONTENT_TYPE_HEADER } from "./constants.js"
 
-export function extractContentType(headers: Record<string, string> = {}): string | undefined {
-  return Object.entries(headers).find(([k]) =>
+export function extractContentType(headers: HeadersInit = {}): string | undefined {
+  const normalizedHeaders = headers instanceof Array ? Object.fromEntries(headers) : headers
+  return Object.entries(normalizedHeaders).find(([k]) =>
     k.toLowerCase() === CONTENT_TYPE_HEADER.toLowerCase()
   )?.[1]
 }
diff --git a/test/deno/wretch_test.ts b/test/deno/wretch_test.ts
index cd2c09f..b4b0bab 100644
--- a/test/deno/wretch_test.ts
+++ b/test/deno/wretch_test.ts
@@ -1,12 +1,12 @@
 import {
   assertEquals,
   fail
-} from "https://deno.land/std@0.147.0/testing/asserts.ts"
+} from "jsr:@std/assert"
 import {
   beforeAll,
   describe,
   it,
-} from "https://deno.land/std@0.147.0/testing/bdd.ts"
+} from "jsr:@std/testing/bdd"
 
 import wretchFn from "../../dist/bundle/wretch.min.mjs"
 import BasicAuthAddon from "../../dist/bundle/addons/basicAuth.min.mjs"
@@ -15,7 +15,7 @@ import FormDataAddon from "../../dist/bundle/addons/formData.min.mjs"
 import QueryAddon from "../../dist/bundle/addons/queryString.min.mjs"
 import AbortAddon from "../../dist/bundle/addons/abort.min.mjs"
 // import PerfsAddon from "../../dist/bundle/addons/perfs.min.mjs"
-import type { Wretch, WretchResponseChain, WretchResponse, Middleware } from "../../dist/types.d.ts"
+import type { Wretch, WretchResponseChain, WretchResponse, Middleware, WretchError } from "../../dist/types.d.ts"
 
 declare type factory = {
   (_url?: string, _options?: object): Wretch;
@@ -117,7 +117,7 @@ describe("Wretch", function () {
     }
     // Ensure that the charset is preserved.
     const headerWithCharset = "application/json; charset=utf-16"
-    assertEquals((wretch()).content(headerWithCharset).json({})._options.headers["Content-Type"], headerWithCharset)
+    assertEquals((wretch()).content(headerWithCharset).json({})._options.headers?.["Content-Type" as keyof HeadersInit], headerWithCharset)
   })
 
   it("should perform an url encoded form data round trip", async function () {
@@ -395,7 +395,7 @@ describe("Wretch", function () {
         await wretch(_URL + "/basicauth")
           .get()
           .res(_ => fail("Authenticated route should not respond without credentials."))
-      } catch (e) {
+      } catch (e: any) {
         assertEquals(e.status, 401)
       }
     })
diff --git a/test/node/middlewares/retry.spec.ts b/test/node/middlewares/retry.spec.ts
index e609c7f..2e52949 100644
--- a/test/node/middlewares/retry.spec.ts
+++ b/test/node/middlewares/retry.spec.ts
@@ -99,7 +99,7 @@ export default describe("Retry Middleware", () => {
         true
       )
       .options({ a: 1 })
-    await expect(w.get("/retry").res()).rejects.toThrowError(
+    await expect(w.get("/retry").res()).rejects.toThrow(
       "Number of attempts exceeded."
     )
     expect(counter).toEqual(10)
@@ -114,17 +114,17 @@ export default describe("Retry Middleware", () => {
           delayTimer: 1,
           onRetry() {
             counter++
-            return { url: `/${counter}`, options: { method: counter } }
+            return { url: `/${counter}`, options: { method: `${counter}` } }
           },
         }),
       ],
       true
     )
-    await expect(w.options({ a: 0 }).get("/0").res()).rejects.toThrowError(
+    await expect(w.options({ a: 0 }).get("/0").res()).rejects.toThrow(
       "Number of attempts exceeded."
     )
     logs.forEach((log, index) => {
-      expect(log).toMatchObject([`/${index}`, index === 0 ? "GET" : index])
+      expect(log).toMatchObject([`/${index}`, index === 0 ? "GET" : `${index}`])
     })
   })
 
@@ -161,10 +161,10 @@ export default describe("Retry Middleware", () => {
         true
       )
 
-    await expect(wThrow.get("/retry").res()).rejects.toThrowError(
+    await expect(wThrow.get("/retry").res()).rejects.toThrow(
       "Network Error"
     )
-    await expect(wRetry.get("/retry").res()).rejects.toThrowError(
+    await expect(wRetry.get("/retry").res()).rejects.toThrow(
       "Network Error"
     )
     expect(counter).toBe(10)