diff --git a/src/Internal/Response.php b/src/Internal/Response.php
index aca7b58..5cc31d0 100644
--- a/src/Internal/Response.php
+++ b/src/Internal/Response.php
@@ -20,7 +20,9 @@ private function __construct(
 
     public static function from(HttpCode $code, mixed $data, array $headers): ResponseInterface
     {
-        $headers = empty($headers) ? ['Content-Type' => 'application/json'] : $headers;
+        if (empty($headers)) {
+            $headers[] = ['Content-Type' => 'application/json'];
+        }
 
         return new Response(code: $code, body: StreamFactory::from(data: $data), headers: $headers);
     }
diff --git a/tests/HttpResponseTest.php b/tests/HttpResponseTest.php
index 5395a3c..dd01ab9 100644
--- a/tests/HttpResponseTest.php
+++ b/tests/HttpResponseTest.php
@@ -8,7 +8,7 @@
 
 class HttpResponseTest extends TestCase
 {
-    private array $defaultHeader = ['Content-Type' => 'application/json'];
+    private array $defaultHeader = [['Content-Type' => 'application/json']];
 
     /**
      * @dataProvider providerData