diff --git a/src/ServerUrlMiddleware.php b/src/ServerUrlMiddleware.php
index bf85867..c3c100b 100644
--- a/src/ServerUrlMiddleware.php
+++ b/src/ServerUrlMiddleware.php
@@ -12,7 +12,7 @@
 
 class ServerUrlMiddleware implements MiddlewareInterface
 {
-    public function __construct(private ServerUrlHelper $helper)
+    public function __construct(private readonly ServerUrlHelper $helper)
     {
     }
 
diff --git a/src/UrlHelper.php b/src/UrlHelper.php
index f79b465..326fb58 100644
--- a/src/UrlHelper.php
+++ b/src/UrlHelper.php
@@ -37,7 +37,7 @@ class UrlHelper implements UrlHelperInterface
 
     private ?ServerRequestInterface $request = null;
 
-    public function __construct(private RouterInterface $router)
+    public function __construct(private readonly RouterInterface $router)
     {
     }
 
diff --git a/src/UrlHelperFactory.php b/src/UrlHelperFactory.php
index da3ffb7..7fe2fa9 100644
--- a/src/UrlHelperFactory.php
+++ b/src/UrlHelperFactory.php
@@ -33,8 +33,8 @@ public static function __set_state(array $data): self
      * @param string $basePath Base path for the URL helper
      */
     public function __construct(
-        private string $basePath = '/',
-        private string $routerServiceName = RouterInterface::class
+        private readonly string $basePath = '/',
+        private readonly string $routerServiceName = RouterInterface::class
     ) {
     }
 
diff --git a/src/UrlHelperMiddleware.php b/src/UrlHelperMiddleware.php
index 5b9f4bb..68d6db5 100644
--- a/src/UrlHelperMiddleware.php
+++ b/src/UrlHelperMiddleware.php
@@ -15,7 +15,7 @@
  */
 class UrlHelperMiddleware implements MiddlewareInterface
 {
-    public function __construct(private UrlHelperInterface $helper)
+    public function __construct(private readonly UrlHelperInterface $helper)
     {
     }
 
diff --git a/src/UrlHelperMiddlewareFactory.php b/src/UrlHelperMiddlewareFactory.php
index 7b64f5c..5cc3dad 100644
--- a/src/UrlHelperMiddlewareFactory.php
+++ b/src/UrlHelperMiddlewareFactory.php
@@ -26,7 +26,7 @@ public static function __set_state(array $data): self
     /**
      * Allow varying behavior based on URL helper service name.
      */
-    public function __construct(private string $urlHelperServiceName = UrlHelper::class)
+    public function __construct(private readonly string $urlHelperServiceName = UrlHelper::class)
     {
     }
 
diff --git a/test/RequestHandler.php b/test/RequestHandler.php
index 6f2b68c..5336e0c 100644
--- a/test/RequestHandler.php
+++ b/test/RequestHandler.php
@@ -13,7 +13,7 @@
 final class RequestHandler implements RequestHandlerInterface
 {
     private ?ServerRequestInterface $received = null;
-    private ResponseInterface $defaultResponse;
+    private readonly ResponseInterface $defaultResponse;
 
     public function __construct(
         ResponseInterface|null $defaultResponse = null,