diff --git a/classes/DefaultArgumentRemoverReturnTypes100.php b/classes/DefaultArgumentRemoverReturnTypes100.php
index c32dcbb..57b2218 100644
--- a/classes/DefaultArgumentRemoverReturnTypes100.php
+++ b/classes/DefaultArgumentRemoverReturnTypes100.php
@@ -98,13 +98,13 @@ public static function removeDefaultArgumentsWithReflection(Invocation $invocati
         $reflection = new ReflectionClass($invocation);
 
         $reflectionReturnType = $reflection->getProperty('returnType');
-        $reflectionReturnType->setAccessible(true);
+        ReflectionHelper::setAccessible($reflectionReturnType);
 
         $reflectionIsOptional = $reflection->getProperty('isReturnTypeNullable');
-        $reflectionIsOptional->setAccessible(true);
+        ReflectionHelper::setAccessible($reflectionIsOptional);
 
         $reflectionIsProxied = $reflection->getProperty('proxiedCall');
-        $reflectionIsProxied->setAccessible(true);
+        ReflectionHelper::setAccessible($reflectionIsProxied);
 
         $returnType = $reflectionReturnType->getValue($invocation);
         $proxiedCall = $reflectionIsProxied->getValue($invocation);
diff --git a/classes/DefaultArgumentRemoverReturnTypes120.php b/classes/DefaultArgumentRemoverReturnTypes120.php
index 8cce8fa..e41d2e3 100644
--- a/classes/DefaultArgumentRemoverReturnTypes120.php
+++ b/classes/DefaultArgumentRemoverReturnTypes120.php
@@ -98,10 +98,10 @@ public static function removeDefaultArgumentsWithReflection(Invocation $invocati
         $reflection = new ReflectionClass($invocation);
 
         $reflectionReturnType = $reflection->getProperty('returnType');
-        $reflectionReturnType->setAccessible(true);
+        ReflectionHelper::setAccessible($reflectionReturnType);
 
         $reflectionIsOptional = $reflection->getProperty('isReturnTypeNullable');
-        $reflectionIsOptional->setAccessible(true);
+        ReflectionHelper::setAccessible($reflectionIsOptional);
 
         $returnType = $reflectionReturnType->getValue($invocation);
 
diff --git a/classes/PHPMock.php b/classes/PHPMock.php
index c75a9d3..13e4a0c 100644
--- a/classes/PHPMock.php
+++ b/classes/PHPMock.php
@@ -116,19 +116,19 @@ public function registerForTearDown(Deactivatable $deactivatable)
             $facade = Facade::instance();
 
             $property = new ReflectionProperty(Facade::class, 'sealed');
-            $property->setAccessible(true);
+            ReflectionHelper::setAccessible($property);
             $property->setValue($facade, false);
 
             $method = new ReflectionMethod($facade, 'deferredDispatcher');
-            $method->setAccessible(true);
+            ReflectionHelper::setAccessible($method);
             $dispatcher = $method->invoke($facade);
 
             $propDispatcher = new ReflectionProperty($dispatcher, 'dispatcher');
-            $propDispatcher->setAccessible(true);
+            ReflectionHelper::setAccessible($propDispatcher);
             $directDispatcher = $propDispatcher->getValue($dispatcher);
 
             $propSubscribers = new ReflectionProperty($directDispatcher, 'subscribers');
-            $propSubscribers->setAccessible(true);
+            ReflectionHelper::setAccessible($propSubscribers);
 
             $facade->registerSubscriber(
                 new MockDisabler(
@@ -239,7 +239,7 @@ private function prepareCustomTemplates()
                 $reflection = new ReflectionClass($mockMethodClass);
 
                 $reflectionTemplates = $reflection->getProperty('templates');
-                $reflectionTemplates->setAccessible(true);
+                ReflectionHelper::setAccessible($reflectionTemplates);
 
                 $reflectionTemplates->setValue(null, $templates);
 
diff --git a/classes/ReflectionHelper.php b/classes/ReflectionHelper.php
new file mode 100644
index 0000000..a65e827
--- /dev/null
+++ b/classes/ReflectionHelper.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace phpmock\phpunit;
+
+/**
+ * @internal
+ */
+final class ReflectionHelper
+{
+    private function __construct()
+    {
+    }
+
+    public static function setAccessible($reflection)
+    {
+        // As of PHP 8.1.0, reflection setAccessible is no-op; all properties are accessible by default.
+        if (PHP_VERSION_ID >= 80100) {
+            return;
+        }
+
+        $reflection->setAccessible(true);
+    }
+}
diff --git a/phpunit.xml b/phpunit.xml
index 203311b..17ace8f 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,6 +1,7 @@
 <phpunit
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/4.3/phpunit.xsd"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         displayDetailsOnTestsThatTriggerDeprecations="true"
          bootstrap="vendor/autoload.php">
     <testsuite name="Unit tests">
         <directory>tests/</directory>
diff --git a/tests/MockObjectProxyTest.php b/tests/MockObjectProxyTest.php
index e9f35e4..40c52a8 100644
--- a/tests/MockObjectProxyTest.php
+++ b/tests/MockObjectProxyTest.php
@@ -91,7 +91,7 @@ private function getMethodMatcher($invocationMocker)
         ) {
             $reflection = new \ReflectionClass(InvocationMocker::class);
             $property = $reflection->getProperty('matcher');
-            $property->setAccessible(true);
+            ReflectionHelper::setAccessible($property);
             return $property->getValue($invocationMocker)->methodNameRule();
         }
 
@@ -100,7 +100,7 @@ private function getMethodMatcher($invocationMocker)
         ) {
             $reflection = new \ReflectionClass(InvocationMocker::class);
             $property = $reflection->getProperty('matcher');
-            $property->setAccessible(true);
+            ReflectionHelper::setAccessible($property);
             return $property->getValue($invocationMocker)->getMethodNameRule();
         }