diff --git a/composer.json b/composer.json
index 949f84d923..bb599f2001 100644
--- a/composer.json
+++ b/composer.json
@@ -34,8 +34,8 @@
         "ext-sqlite3": "*",
         "friendsofphp/php-cs-fixer": "^2.19",
         "monolog/monolog": "^2.9",
-        "phpstan/phpstan": "^1.11",
-        "phpstan/phpstan-phpunit": "^1.4",
+        "phpstan/phpstan": "^2.1",
+        "phpstan/phpstan-phpunit": "^2.0",
         "phpunit/phpunit": "^9.6"
     },
     "suggest" : {
@@ -63,7 +63,7 @@
     ],
     "scripts": {
         "phpstan": [
-            "phpstan analyse lib tests"
+            "phpstan analyse lib tests --memory-limit 256M"
         ],
         "cs-fixer": [
             "php-cs-fixer fix"
diff --git a/phpstan.neon b/phpstan.neon
index 2026e1d84b..176438a231 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -1,5 +1,8 @@
 parameters:
   level: 1
+  phpVersion:
+      min: 70400
+      max: 80500
   bootstrapFiles:
     - tests/bootstrap.php
   ignoreErrors:
@@ -8,4 +11,4 @@ parameters:
       path: tests/*
 includes:
   - vendor/phpstan/phpstan-phpunit/extension.neon
-  - vendor/phpstan/phpstan-phpunit/rules.neon
\ No newline at end of file
+  - vendor/phpstan/phpstan-phpunit/rules.neon
diff --git a/tests/Sabre/CalDAV/CalendarObjectTest.php b/tests/Sabre/CalDAV/CalendarObjectTest.php
index 3ac118ce19..bc18099ce5 100644
--- a/tests/Sabre/CalDAV/CalendarObjectTest.php
+++ b/tests/Sabre/CalDAV/CalendarObjectTest.php
@@ -9,11 +9,11 @@ class CalendarObjectTest extends \PHPUnit\Framework\TestCase
     /**
      * @var Sabre\CalDAV\Backend_PDO
      */
-    protected $backend;
+    private $backend;
     /**
      * @var Sabre\CalDAV\Calendar
      */
-    protected $calendar;
+    private $calendar;
     protected $principalBackend;
 
     public function setup(): void
diff --git a/tests/Sabre/CalDAV/CalendarTest.php b/tests/Sabre/CalDAV/CalendarTest.php
index c1bdd23b93..3dc2b59b7f 100644
--- a/tests/Sabre/CalDAV/CalendarTest.php
+++ b/tests/Sabre/CalDAV/CalendarTest.php
@@ -11,7 +11,7 @@ class CalendarTest extends \PHPUnit\Framework\TestCase
     /**
      * @var Sabre\CalDAV\Backend\PDO
      */
-    protected $backend;
+    private $backend;
     protected $principalBackend;
     /**
      * @var Sabre\CalDAV\Calendar
diff --git a/tests/Sabre/CalDAV/Schedule/SchedulingObjectTest.php b/tests/Sabre/CalDAV/Schedule/SchedulingObjectTest.php
index 732e6d1703..aed59065ef 100644
--- a/tests/Sabre/CalDAV/Schedule/SchedulingObjectTest.php
+++ b/tests/Sabre/CalDAV/Schedule/SchedulingObjectTest.php
@@ -11,7 +11,7 @@ class SchedulingObjectTest extends \PHPUnit\Framework\TestCase
     /**
      * @var Sabre\CalDAV\Backend_PDO
      */
-    protected $backend;
+    private $backend;
     /**
      * @var Sabre\CalDAV\Calendar
      */
@@ -19,7 +19,7 @@ class SchedulingObjectTest extends \PHPUnit\Framework\TestCase
     /**
      * @var Inbox
      */
-    protected $inbox;
+    private $inbox;
     protected $principalBackend;
 
     protected $data;