diff --git a/src/Browser/HttpOptions.php b/src/Browser/HttpOptions.php
index 7ca5840..c3ecf61 100644
--- a/src/Browser/HttpOptions.php
+++ b/src/Browser/HttpOptions.php
@@ -214,19 +214,27 @@ final public function files(): array
     final public function server(): array
     {
         $server = $this->options['server'];
-        $headers = $this->options['headers'];
+        $headers = \array_combine(
+            \array_map(
+                static fn($header) => \mb_strtoupper(\str_replace('-', '_', $header)),
+                \array_keys($this->options['headers'])
+            ),
+            $this->options['headers']
+        );
+
+        if (null !== $this->options['json'] && !\array_key_exists('ACCEPT', $headers)) {
+            $headers['ACCEPT'] = 'application/json';
+        }
 
-        if (null !== $this->options['json']) {
-            $headers['Content-Type'] = $headers['Accept'] = 'application/json';
+        if (null !== $this->options['json'] && !\array_key_exists('CONTENT_TYPE', $headers)) {
+            $headers['CONTENT_TYPE'] = 'application/json';
         }
 
-        if (false !== $this->options['ajax']) {
-            $headers['X-Requested-With'] = 'XMLHttpRequest';
+        if (false !== $this->options['ajax'] && !\array_key_exists('X_REQUESTED_WITH', $headers)) {
+            $headers['X_REQUESTED_WITH'] = 'XMLHttpRequest';
         }
 
         foreach ($headers as $header => $value) {
-            $header = \mb_strtoupper(\str_replace('-', '_', $header));
-
             // content type header cannot have HTTP_ prefix
             if ('CONTENT_TYPE' !== $header) {
                 $header = "HTTP_{$header}";
diff --git a/tests/BrowserKitBrowserTests.php b/tests/BrowserKitBrowserTests.php
index a61bd97..b83e9eb 100644
--- a/tests/BrowserKitBrowserTests.php
+++ b/tests/BrowserKitBrowserTests.php
@@ -204,6 +204,8 @@ public function http_method_actions(): void
             ->post('/http-method', CustomHttpOptions::api('my-token'))
             ->assertContains('"content-type":["application\/json"]')
             ->assertContains('"x-token":["my-token"]')
+            ->post('/http-method', HttpOptions::json()->withHeader('content-type', 'application/ld+json'))
+            ->assertContains('"content-type":["application\/ld+json"]')
         ;
     }
 
diff --git a/tests/HttpOptionsTest.php b/tests/HttpOptionsTest.php
index f6e3de7..ff39599 100644
--- a/tests/HttpOptionsTest.php
+++ b/tests/HttpOptionsTest.php
@@ -256,4 +256,26 @@ public function can_merge_with_http_options_object(): void
             $options->server()
         );
     }
+
+    /**
+     * @test
+     */
+    public function can_override_json_and_ajax_headers(): void
+    {
+        $options = HttpOptions::jsonAjax()
+            ->withHeader('Accept', 'application/ld+json')
+            ->withHeader('Content-Type', 'application/ld+json')
+            ->withHeader('X-Requested-With', 'something')
+        ;
+
+        $this->assertNull($options->body());
+        $this->assertSame(
+            [
+                'HTTP_ACCEPT' => 'application/ld+json',
+                'CONTENT_TYPE' => 'application/ld+json',
+                'HTTP_X_REQUESTED_WITH' => 'something',
+            ],
+            $options->server()
+        );
+    }
 }