diff --git a/src/Router/Entities/JsonResponse.php b/src/Router/Entities/JsonResponse.php
index 605212f..a70a9da 100644
--- a/src/Router/Entities/JsonResponse.php
+++ b/src/Router/Entities/JsonResponse.php
@@ -4,17 +4,18 @@
 
 namespace Gacela\Router\Entities;
 
+use function in_array;
+
 final class JsonResponse extends Response
 {
+    /**
+     * @param list<string> $headers
+     */
     public function __construct(array $json, array $headers = [])
     {
+        if (!in_array('Content-Type: application/json', $headers, true)) {
+            $headers[] = 'Content-Type: application/json';
+        }
         parent::__construct(json_encode($json, JSON_THROW_ON_ERROR), $headers);
     }
-
-    public function __toString(): string
-    {
-        header('Content-Type: application/json');
-
-        return parent::__toString();
-    }
 }
diff --git a/tests/Feature/Router/RouterResponseTest.php b/tests/Feature/Router/RouterResponseTest.php
index bc75fab..8a2c0d5 100644
--- a/tests/Feature/Router/RouterResponseTest.php
+++ b/tests/Feature/Router/RouterResponseTest.php
@@ -76,4 +76,32 @@ public function test_response_headers(): void
             ],
         ], $this->headers());
     }
+
+    public function test_json_response_headers(): void
+    {
+        $_SERVER['REQUEST_URI'] = 'https://example.org/uri';
+        $_SERVER['REQUEST_METHOD'] = Request::METHOD_GET;
+
+        Router::configure(static function (Routes $routes): void {
+            $routes->get('uri', static fn () => new JsonResponse(['key' => 'value'], [
+                'Access-Control-Allow-Origin: *',
+                'Content-Type: application/json',
+            ]));
+        });
+
+        $this->expectOutputString('{"key":"value"}');
+
+        self::assertSame([
+            [
+                'header' => 'Access-Control-Allow-Origin: *',
+                'replace' => true,
+                'response_code' => 0,
+            ],
+            [
+                'header' => 'Content-Type: application/json',
+                'replace' => true,
+                'response_code' => 0,
+            ],
+        ], $this->headers());
+    }
 }