diff --git a/src/CsrfMiddleware.php b/src/CsrfMiddleware.php
index 5dcd2e4..2468af1 100644
--- a/src/CsrfMiddleware.php
+++ b/src/CsrfMiddleware.php
@@ -25,8 +25,8 @@ class CsrfMiddleware implements MiddlewareInterface
     public const GUARD_ATTRIBUTE = 'csrf';
 
     public function __construct(
-        private CsrfGuardFactoryInterface $guardFactory,
-        private string $attributeKey = self::GUARD_ATTRIBUTE
+        private readonly CsrfGuardFactoryInterface $guardFactory,
+        private readonly string $attributeKey = self::GUARD_ATTRIBUTE
     ) {
     }
 
diff --git a/src/FlashCsrfGuard.php b/src/FlashCsrfGuard.php
index 461eeca..63c0961 100644
--- a/src/FlashCsrfGuard.php
+++ b/src/FlashCsrfGuard.php
@@ -11,7 +11,7 @@
 
 class FlashCsrfGuard implements CsrfGuardInterface
 {
-    public function __construct(private FlashMessagesInterface $flashMessages)
+    public function __construct(private readonly FlashMessagesInterface $flashMessages)
     {
     }
 
diff --git a/src/FlashCsrfGuardFactory.php b/src/FlashCsrfGuardFactory.php
index 6183420..1fe0a7d 100644
--- a/src/FlashCsrfGuardFactory.php
+++ b/src/FlashCsrfGuardFactory.php
@@ -10,7 +10,7 @@
 
 class FlashCsrfGuardFactory implements CsrfGuardFactoryInterface
 {
-    public function __construct(private string $attributeKey = FlashMessageMiddleware::FLASH_ATTRIBUTE)
+    public function __construct(private readonly string $attributeKey = FlashMessageMiddleware::FLASH_ATTRIBUTE)
     {
     }
 
diff --git a/src/SessionCsrfGuard.php b/src/SessionCsrfGuard.php
index 015f19f..c905020 100644
--- a/src/SessionCsrfGuard.php
+++ b/src/SessionCsrfGuard.php
@@ -11,7 +11,7 @@
 
 class SessionCsrfGuard implements CsrfGuardInterface
 {
-    public function __construct(private SessionInterface $session)
+    public function __construct(private readonly SessionInterface $session)
     {
     }
 
diff --git a/src/SessionCsrfGuardFactory.php b/src/SessionCsrfGuardFactory.php
index 6a3dea3..323a77b 100644
--- a/src/SessionCsrfGuardFactory.php
+++ b/src/SessionCsrfGuardFactory.php
@@ -10,7 +10,7 @@
 
 class SessionCsrfGuardFactory implements CsrfGuardFactoryInterface
 {
-    public function __construct(private string $attributeKey = SessionMiddleware::SESSION_ATTRIBUTE)
+    public function __construct(private readonly string $attributeKey = SessionMiddleware::SESSION_ATTRIBUTE)
     {
     }