diff --git a/src/App/src/Handler/HomePageHandler.php b/src/App/src/Handler/HomePageHandler.php
index dc629a7..0b35cfe 100644
--- a/src/App/src/Handler/HomePageHandler.php
+++ b/src/App/src/Handler/HomePageHandler.php
@@ -24,9 +24,9 @@
 class HomePageHandler implements RequestHandlerInterface
 {
     public function __construct(
-        private string $containerName,
-        private RouterInterface $router,
-        private ?TemplateRendererInterface $template = null
+        private readonly string $containerName,
+        private readonly RouterInterface $router,
+        private readonly ?TemplateRendererInterface $template = null
     ) {
     }
 
diff --git a/src/MezzioInstaller/OptionalPackages.php b/src/MezzioInstaller/OptionalPackages.php
index a39588a..5270dca 100644
--- a/src/MezzioInstaller/OptionalPackages.php
+++ b/src/MezzioInstaller/OptionalPackages.php
@@ -175,7 +175,7 @@ class OptionalPackages
     ];
 
     /** @var string Path to this file. */
-    private string $installerSource;
+    private readonly string $installerSource;
 
     /** @var self::INSTALL_* Installation type selected. */
     private string $installType = self::INSTALL_FLAT;
@@ -214,8 +214,11 @@ public static function install(Event $event): void
         $installer->finalizePackage();
     }
 
-    public function __construct(private IOInterface $io, private Composer $composer, ?string $projectRoot = null)
-    {
+    public function __construct(
+        private readonly IOInterface $io,
+        private readonly Composer $composer,
+        ?string $projectRoot = null
+    ) {
         // Get composer.json location
         $composerFile = Factory::getComposerFile();
 
diff --git a/test/MezzioInstallerTest/OptionalPackagesTestCase.php b/test/MezzioInstallerTest/OptionalPackagesTestCase.php
index 2216347..306bc95 100644
--- a/test/MezzioInstallerTest/OptionalPackagesTestCase.php
+++ b/test/MezzioInstallerTest/OptionalPackagesTestCase.php
@@ -54,8 +54,8 @@ public static function assertPackage(
         OptionalPackages $installer,
         ?string $message = null
     ): void {
-        $message = $message ?? sprintf('Failed asserting that package "%s" is present in the installer', $package);
-        $found   = false;
+        $message ??= sprintf('Failed asserting that package "%s" is present in the installer', $package);
+        $found     = false;
 
         foreach (['composerRequires', 'composerDevRequires'] as $property) {
             $r = new ReflectionProperty($installer, $property);
@@ -78,8 +78,8 @@ public static function assertNotPackage(
         OptionalPackages $installer,
         ?string $message = null
     ): void {
-        $message = $message ?? sprintf('Failed asserting that package "%s" is absent from the installer', $package);
-        $found   = false;
+        $message ??= sprintf('Failed asserting that package "%s" is absent from the installer', $package);
+        $found     = false;
 
         foreach (['composerRequires', 'composerDevRequires'] as $property) {
             $r = new ReflectionProperty($installer, $property);
@@ -134,8 +134,8 @@ public static function assertWhitelisted(
         OptionalPackages $installer,
         ?string $message = null
     ): void {
-        $message = $message ?? sprintf('Failed asserting that package "%s" is whitelisted in composer.json', $package);
-        $found   = false;
+        $message ??= sprintf('Failed asserting that package "%s" is whitelisted in composer.json', $package);
+        $found     = false;
 
         $r = new ReflectionProperty($installer, 'composerDefinition');
 
@@ -167,8 +167,8 @@ protected function tearDown(): void
      */
     protected function createOptionalPackages(?string $projectRoot = null): OptionalPackages
     {
-        $projectRoot = $projectRoot ?? $this->packageRoot;
-        $this->io    = $this->createMock(IOInterface::class);
+        $projectRoot ??= $this->packageRoot;
+        $this->io      = $this->createMock(IOInterface::class);
         return new OptionalPackages(
             $this->io,
             $this->createComposer(),