diff --git a/deno.json b/deno.json
index 83c2ac7..fe1cfd2 100644
--- a/deno.json
+++ b/deno.json
@@ -8,8 +8,8 @@
   },
   "imports": {
     "@deno/dnt": "jsr:@deno/dnt@^0.41.3",
-    "@std/expect": "jsr:@std/expect@^1.0.6",
-    "@std/testing": "jsr:@std/testing@^1.0.3",
+    "@std/expect": "jsr:@std/expect@^1.0.9",
+    "@std/testing": "jsr:@std/testing@^1.0.6",
     "#fetch": "./src/fetch/mod.ts",
     "#response": "./src/response/mod.ts"
   },
diff --git a/deno.lock b/deno.lock
index 1576f10..61c9ae9 100644
--- a/deno.lock
+++ b/deno.lock
@@ -7,26 +7,27 @@
     "jsr:@deno/graph@~0.73.1": "0.73.1",
     "jsr:@std/assert@0.223": "0.223.0",
     "jsr:@std/assert@0.226": "0.226.0",
-    "jsr:@std/assert@^1.0.6": "1.0.6",
-    "jsr:@std/async@^1.0.5": "1.0.7",
+    "jsr:@std/assert@^1.0.9": "1.0.9",
     "jsr:@std/bytes@0.223": "0.223.0",
     "jsr:@std/data-structures@^1.0.4": "1.0.4",
-    "jsr:@std/expect@^1.0.6": "1.0.6",
+    "jsr:@std/expect@^1.0.9": "1.0.9",
     "jsr:@std/fmt@0.223": "0.223.0",
     "jsr:@std/fmt@1": "1.0.3",
     "jsr:@std/fs@0.223": "0.223.0",
-    "jsr:@std/fs@1": "1.0.5",
+    "jsr:@std/fs@1": "1.0.6",
     "jsr:@std/fs@^1.0.4": "1.0.5",
+    "jsr:@std/fs@^1.0.6": "1.0.6",
     "jsr:@std/fs@~0.229.3": "0.229.3",
-    "jsr:@std/internal@^1.0.4": "1.0.4",
+    "jsr:@std/internal@^1.0.5": "1.0.5",
     "jsr:@std/io@0.223": "0.223.0",
     "jsr:@std/path@0.223": "0.223.0",
-    "jsr:@std/path@1": "1.0.7",
+    "jsr:@std/path@1": "1.0.8",
     "jsr:@std/path@1.0.0-rc.1": "1.0.0-rc.1",
     "jsr:@std/path@^1.0.6": "1.0.7",
-    "jsr:@std/path@^1.0.7": "1.0.7",
+    "jsr:@std/path@^1.0.7": "1.0.8",
+    "jsr:@std/path@^1.0.8": "1.0.8",
     "jsr:@std/path@~0.225.2": "0.225.2",
-    "jsr:@std/testing@^1.0.3": "1.0.3",
+    "jsr:@std/testing@^1.0.6": "1.0.6",
     "jsr:@ts-morph/bootstrap@0.24": "0.24.0",
     "jsr:@ts-morph/common@0.24": "0.24.0"
   },
@@ -64,25 +65,22 @@
     "@std/assert@0.226.0": {
       "integrity": "0dfb5f7c7723c18cec118e080fec76ce15b4c31154b15ad2bd74822603ef75b3"
     },
-    "@std/assert@1.0.6": {
-      "integrity": "1904c05806a25d94fe791d6d883b685c9e2dcd60e4f9fc30f4fc5cf010c72207",
+    "@std/assert@1.0.9": {
+      "integrity": "a9f0c611a869cc791b26f523eec54c7e187aab7932c2c8e8bea0622d13680dcd",
       "dependencies": [
         "jsr:@std/internal"
       ]
     },
-    "@std/async@1.0.7": {
-      "integrity": "f4fadc0124432e37cba11e8b3880164661a664de00a65118d976848f32f96290"
-    },
     "@std/bytes@0.223.0": {
       "integrity": "84b75052cd8680942c397c2631318772b295019098f40aac5c36cead4cba51a8"
     },
     "@std/data-structures@1.0.4": {
       "integrity": "fa0e20c11eb9ba673417450915c750a0001405a784e2a4e0c3725031681684a0"
     },
-    "@std/expect@1.0.6": {
-      "integrity": "dffba969ca5ea6d7c39338d4985c9af2bfa6e080c710cc2b77756dd7657c369c",
+    "@std/expect@1.0.9": {
+      "integrity": "108bb428f17492ac40439479e1dc55fbaae581530e905a8603f97305842a5a01",
       "dependencies": [
-        "jsr:@std/assert@^1.0.6",
+        "jsr:@std/assert@^1.0.9",
         "jsr:@std/internal"
       ]
     },
@@ -107,8 +105,14 @@
         "jsr:@std/path@^1.0.7"
       ]
     },
-    "@std/internal@1.0.4": {
-      "integrity": "62e8e4911527e5e4f307741a795c0b0a9e6958d0b3790716ae71ce085f755422"
+    "@std/fs@1.0.6": {
+      "integrity": "42b56e1e41b75583a21d5a37f6a6a27de9f510bcd36c0c85791d685ca0b85fa2",
+      "dependencies": [
+        "jsr:@std/path@^1.0.8"
+      ]
+    },
+    "@std/internal@1.0.5": {
+      "integrity": "54a546004f769c1ac9e025abd15a76b6671ddc9687e2313b67376125650dc7ba"
     },
     "@std/io@0.223.0": {
       "integrity": "2d8c3c2ab3a515619b90da2c6ff5ea7b75a94383259ef4d02116b228393f84f1",
@@ -135,15 +139,17 @@
     "@std/path@1.0.7": {
       "integrity": "76a689e07f0e15dcc6002ec39d0866797e7156629212b28f27179b8a5c3b33a1"
     },
-    "@std/testing@1.0.3": {
-      "integrity": "f98c2bee53860a5916727d7e7d3abe920dd6f9edace022e2d059f00d05c2cf42",
+    "@std/path@1.0.8": {
+      "integrity": "548fa456bb6a04d3c1a1e7477986b6cffbce95102d0bb447c67c4ee70e0364be"
+    },
+    "@std/testing@1.0.6": {
+      "integrity": "9192ded2d34065f4c959fdc1921fe836770abb9194410c2cc8a0fff4eff5c893",
       "dependencies": [
-        "jsr:@std/assert@^1.0.6",
-        "jsr:@std/async",
+        "jsr:@std/assert@^1.0.9",
         "jsr:@std/data-structures",
-        "jsr:@std/fs@^1.0.4",
+        "jsr:@std/fs@^1.0.6",
         "jsr:@std/internal",
-        "jsr:@std/path@^1.0.6"
+        "jsr:@std/path@^1.0.8"
       ]
     },
     "@ts-morph/bootstrap@0.24.0": {
@@ -163,8 +169,8 @@
   "workspace": {
     "dependencies": [
       "jsr:@deno/dnt@~0.41.3",
-      "jsr:@std/expect@^1.0.6",
-      "jsr:@std/testing@^1.0.3"
+      "jsr:@std/expect@^1.0.9",
+      "jsr:@std/testing@^1.0.6"
     ]
   }
 }
diff --git a/src/fetch/__test__/applyMiddleware.test.ts b/src/fetch/__test__/applyMiddleware.test.ts
index a5bde49..32749cf 100644
--- a/src/fetch/__test__/applyMiddleware.test.ts
+++ b/src/fetch/__test__/applyMiddleware.test.ts
@@ -1,9 +1,9 @@
-import { it } from '@std/testing/bdd';
+import { test } from '@std/testing/bdd';
 import { expect } from '@std/expect';
 import { applyMiddleware } from '../apply-middleware.ts';
 import type { Middleware } from '../types.ts';
 
-it('should apply middleware in the order in which they are passed', async () => {
+test('should apply middleware in the order in which they are passed', async () => {
   const log: string[] = [];
 
   const foo: Middleware = async (request, next) => {
diff --git a/src/middleware/__test__/default-headers.test.ts b/src/middleware/__test__/default-headers.test.ts
new file mode 100644
index 0000000..0ed6243
--- /dev/null
+++ b/src/middleware/__test__/default-headers.test.ts
@@ -0,0 +1,119 @@
+import { test } from '@std/testing/bdd';
+import { expect } from '@std/expect';
+import { defaultHeaders } from '../default-headers.ts';
+
+test('strategy "set", should be default', async () => {
+  const middleware = defaultHeaders({
+    'content-type': 'application/json',
+  });
+
+  const request = new Request('https://foo.bar', {
+    method: 'POST',
+    body: JSON.stringify({ foo: 'bar' }),
+  });
+
+  expect(request.headers.get('Content-Type')).toBe('text/plain;charset=UTF-8');
+
+  const next = (req: Request) => {
+    state.request = req;
+    return new Response('ok');
+  };
+
+  const state: { request: Request | null } = {
+    request: null,
+  };
+
+  await middleware(request, next);
+
+  expect(state.request?.headers.get('Content-Type')).toBe('application/json');
+});
+
+test('strategy "append"', async () => {
+  const middleware = defaultHeaders({
+    'content-type': 'application/json',
+  }, {
+    strategy: 'append',
+  });
+
+  const request = new Request('https://foo.bar', {
+    method: 'POST',
+    body: JSON.stringify({ foo: 'bar' }),
+  });
+
+  expect(request.headers.get('Content-Type')).toBe('text/plain;charset=UTF-8');
+
+  const next = (req: Request) => {
+    state.request = req;
+    return new Response('ok');
+  };
+
+  const state: { request: Request | null } = {
+    request: null,
+  };
+
+  await middleware(request, next);
+
+  expect(state.request?.headers.get('Content-Type')).toBe(
+    'text/plain;charset=UTF-8, application/json',
+  );
+});
+
+test('strategy "defaults-set"', async () => {
+  const middleware = defaultHeaders({
+    'content-type': 'application/json',
+  }, {
+    strategy: 'defaults-set',
+  });
+
+  const request = new Request('https://foo.bar', {
+    method: 'POST',
+    body: JSON.stringify({ foo: 'bar' }),
+  });
+
+  expect(request.headers.get('Content-Type')).toBe('text/plain;charset=UTF-8');
+
+  const next = (req: Request) => {
+    state.request = req;
+    return new Response('ok');
+  };
+
+  const state: { request: Request | null } = {
+    request: null,
+  };
+
+  await middleware(request, next);
+
+  expect(state.request?.headers.get('Content-Type')).toBe(
+    'text/plain;charset=UTF-8',
+  );
+});
+
+test('strategy "defaults-set"', async () => {
+  const middleware = defaultHeaders({
+    'content-type': 'application/json',
+  }, {
+    strategy: 'defaults-append',
+  });
+
+  const request = new Request('https://foo.bar', {
+    method: 'POST',
+    body: JSON.stringify({ foo: 'bar' }),
+  });
+
+  expect(request.headers.get('Content-Type')).toBe('text/plain;charset=UTF-8');
+
+  const next = (req: Request) => {
+    state.request = req;
+    return new Response('ok');
+  };
+
+  const state: { request: Request | null } = {
+    request: null,
+  };
+
+  await middleware(request, next);
+
+  expect(state.request?.headers.get('Content-Type')).toBe(
+    'application/json, text/plain;charset=UTF-8',
+  );
+});
diff --git a/src/middleware/__test__/retry.test.ts b/src/middleware/__test__/retry.test.ts
index d733c2a..46a0914 100644
--- a/src/middleware/__test__/retry.test.ts
+++ b/src/middleware/__test__/retry.test.ts
@@ -1,4 +1,4 @@
-import { afterAll, beforeAll, it } from '@std/testing/bdd';
+import { afterAll, beforeAll, test } from '@std/testing/bdd';
 import { expect } from '@std/expect';
 import { applyMiddleware, configureFetch } from '#fetch';
 import { retry } from '../retry.ts';
@@ -22,7 +22,7 @@ afterAll(async () => {
   await server.shutdown();
 });
 
-it('Should fetch resource until it returns success response)', async () => {
+test('Should fetch resource until it returns success response)', async () => {
   const fetch = configureFetch(globalThis.fetch, applyMiddleware(retry({ count: 10 })));
 
   expect(serverState.counter).toBe(3);
@@ -37,7 +37,7 @@ it('Should fetch resource until it returns success response)', async () => {
   await dump(response);
 });
 
-it('Should break fetch loop when attempt limit is reached', async () => {
+test('Should break fetch loop when attempt limit is reached', async () => {
   const fetch = configureFetch(globalThis.fetch, applyMiddleware(retry({ count: 2 })));
 
   serverState.counter = 5;
diff --git a/src/middleware/default-headers.ts b/src/middleware/default-headers.ts
index 8f82f91..79fba0e 100644
--- a/src/middleware/default-headers.ts
+++ b/src/middleware/default-headers.ts
@@ -3,11 +3,13 @@ import type { Middleware } from '#fetch';
 /** Options of default headers middleware. */
 export interface DefaultHeadersOptions {
   /**
-   * How to add header to request headers.
-   * - "set" - headers will be added using "set" method
-   * - "append" - headers will be added using "append" method
+   * How to add headers to request headers.
+   * - "set" - `defaults` will be added to `request.headers` using "set" method
+   * - "append" - `defaults` will be added to `request.headers` using "append" method
+   * - "defaults-set" - `request.headers` will be added to `defaults` using "set" method
+   * - "defaults-append" - `request.headers` will be added to `defaults` using "append" method
    */
-  strategy?: 'set' | 'append';
+  strategy?: 'set' | 'append' | 'defaults-set' | 'defaults-append';
 }
 
 /**
@@ -17,24 +19,52 @@ export interface DefaultHeadersOptions {
  */
 export function defaultHeaders(
   defaults: HeadersInit,
-  { strategy = 'append' }: DefaultHeadersOptions = {},
+  { strategy = 'set' }: DefaultHeadersOptions = {},
 ): Middleware {
   return (request, next) => {
+    /**
+     * Previously, there was a different approach here:
+     * headers were created based on "defaults" argument,
+     * then headers from the request were added to them.
+     *
+     * This was done so that the "default headers" were
+     * truly default and were overridden by what was set by
+     * the developer in the request itself.
+     *
+     * But it didn't work well because browser always
+     * had the "Content-Type" header set by default,
+     * which always overridden the option that was in the
+     * middleware factory arguments.
+     *
+     * To fix this, `strategy` option is introduced.
+     */
+
     // IMPORTANT: for avoid mutate request, just create new Headers and Request here
-    const headers = new Headers(request.headers);
+    const headers = new Headers(strategy.startsWith('defaults-') ? defaults : request.headers);
 
-    /*
-      Previously, there was a different approach here: headers were created based on "defaults" argument, then headers from the request were added to them.
+    if (strategy === 'defaults-set') {
+      request.headers.forEach((value, key) => {
+        headers.set(key, value);
+      });
+    }
 
-      This was done so that the "default headers" were truly default and were overridden by what was set by the developer in the request itself.
+    if (strategy === 'defaults-append') {
+      request.headers.forEach((value, key) => {
+        headers.append(key, value);
+      });
+    }
 
-      But it didn't work well because browser always had the "Content-Type" header set by default, which always overridden the option that was in the middleware factory arguments.
+    if (strategy === 'set') {
+      new Headers(defaults).forEach((value, key) => {
+        headers.set(key, value);
+      });
+    }
 
-      To fix this, default headers are now added to the request headers
-    */
-    new Headers(defaults).forEach((value, key) => {
-      headers[strategy](key, value);
-    });
+    if (strategy === 'append') {
+      new Headers(defaults).forEach((value, key) => {
+        headers.append(key, value);
+      });
+    }
 
     return next(new Request(request, { headers }));
   };
diff --git a/src/url/__test__/url.test.ts b/src/url/__test__/url.test.ts
index dbe3d83..35a342b 100644
--- a/src/url/__test__/url.test.ts
+++ b/src/url/__test__/url.test.ts
@@ -1,8 +1,8 @@
-import { it } from '@std/testing/bdd';
+import { test } from '@std/testing/bdd';
 import { expect } from '@std/expect';
 import { resetParams, setParams, withoutParams, withParams } from '../url.ts';
 
-it('withParams', () => {
+test('withParams', () => {
   const input = new URL('http://hello.com?foo=1&bar=2');
 
   expect(input.searchParams.get('foo')).toBe('1');
@@ -15,7 +15,7 @@ it('withParams', () => {
   expect(output.searchParams.get('baz')).toBe('4');
 });
 
-it('withoutParams', () => {
+test('withoutParams', () => {
   const input = new URL('http://hello.com?foo=1&bar=2');
 
   expect(input.searchParams.get('foo')).toBe('1');
@@ -28,7 +28,7 @@ it('withoutParams', () => {
   expect(output.searchParams.get('baz')).toBe(null);
 });
 
-it('setParams', () => {
+test('setParams', () => {
   const input = new URL('http://hello.com?foo=1&bar=2');
 
   expect(input.searchParams.get('foo')).toBe('1');
@@ -42,7 +42,7 @@ it('setParams', () => {
   expect(output.searchParams.get('baz')).toBe('4');
 });
 
-it('resetParams', () => {
+test('resetParams', () => {
   const input = new URL('http://hello.com?foo=1&bar=2');
 
   expect(input.searchParams.get('foo')).toBe('1');