diff --git a/.gitattributes b/.gitattributes
index aa02dc6..7c4f104 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,2 +1,3 @@
 /Tests export-ignore
+/phpstan.neon export-ignore
 /phpunit.xml.dist export-ignore
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 6cf4805..e68a7fe 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -74,3 +74,43 @@ jobs:
 
             - name: Run tests
               run: vendor/bin/phpunit
+
+    phpstan:
+        name: PHPStan PHP ${{ matrix.php }} (Symfony ${{ matrix.symfony }})
+        runs-on: ubuntu-latest
+        strategy:
+          matrix:
+            php:
+              - '8.5'
+            symfony:
+              - '8.1.*'
+
+        steps:
+          - name: Checkout
+            uses: actions/checkout@v4
+
+          - name: Setup PHP
+            uses: shivammathur/setup-php@v2
+            with:
+              php-version: ${{ matrix.php }}
+              tools: flex
+              coverage: none
+
+          - name: Get Composer Cache Directory
+            id: composer-cache
+            run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
+
+          - name: Cache dependencies
+            uses: actions/cache@v4
+            with:
+              path: ${{ steps.composer-cache.outputs.dir }}
+              key: ${{ matrix.php }}-composer-${{ hashFiles('**/composer.json') }}
+              restore-keys: ${{ matrix.php }}-composer-
+
+          - name: Update project dependencies
+            run: composer update --no-progress --ansi --prefer-stable
+            env:
+              SYMFONY_REQUIRE: ${{ matrix.symfony }}
+
+          - name: Run PHPStan
+            run: vendor/bin/phpstan analyze --error-format=github
diff --git a/Partial/Exception/ChildIsNotAnArrayNode.php b/Partial/Exception/ChildIsNotAnArrayNode.php
index 7a16f6d..ca1cb22 100644
--- a/Partial/Exception/ChildIsNotAnArrayNode.php
+++ b/Partial/Exception/ChildIsNotAnArrayNode.php
@@ -6,6 +6,9 @@
 
 class ChildIsNotAnArrayNode extends InvalidNodeNavigation
 {
+    /**
+     * @param non-empty-string $nodeName
+     */
     public function __construct(BaseNode $parentNode, $nodeName)
     {
         parent::__construct(
diff --git a/Partial/Exception/UndefinedChildNode.php b/Partial/Exception/UndefinedChildNode.php
index a0fa22f..0b76f62 100644
--- a/Partial/Exception/UndefinedChildNode.php
+++ b/Partial/Exception/UndefinedChildNode.php
@@ -6,6 +6,9 @@
 
 class UndefinedChildNode extends InvalidNodeNavigation
 {
+    /**
+     * @param non-empty-string $childNodeName
+     */
     public function __construct(NodeInterface $parentNode, $childNodeName)
     {
         parent::__construct(
diff --git a/Partial/PartialNode.php b/Partial/PartialNode.php
index 733c56f..d838ec8 100644
--- a/Partial/PartialNode.php
+++ b/Partial/PartialNode.php
@@ -10,23 +10,14 @@
 
 class PartialNode
 {
-    /**
-     * @var \ReflectionProperty
-     */
-    private static $nodeChildrenProperty;
-
-    /**
-     * @var \ReflectionProperty
-     */
-    private static $nodePrototypeProperty;
+    private static ?\ReflectionProperty $nodeChildrenProperty = null;
 
     /**
      * Provide an ArrayNode instance (e.g. the root node created by a TreeBuilder) and a path that is relevant to you,
      * e.g. "dbal.connections": this will strip every node that is not contained in the given path (e.g. the "orm" node
      * would be removed entirely.
      *
-     * @param ArrayNode $node
-     * @param string    $breadcrumbPath
+     * @param string|null $breadcrumbPath
      */
     public static function excludeEverythingNotInBreadcrumbPath(ArrayNode $node, $breadcrumbPath)
     {
@@ -40,7 +31,10 @@ public static function excludeEverythingNotInBreadcrumbPath(ArrayNode $node, $br
     }
 
     /**
-     * @param array $path
+     * @param list<string> $path
+     *
+     * @throws ChildIsNotAnArrayNode if the child node is not an array node
+     * @throws UndefinedChildNode if the node does not have a child in the given path
      */
     public static function excludeEverythingNotInPath(ArrayNode $node, array $path = [])
     {
@@ -71,15 +65,14 @@ public static function excludeEverythingNotInPath(ArrayNode $node, array $path =
     }
 
     /**
-     * @param ArrayNode $node
-     * @param string    $childNodeName
+     * @param non-empty-string $childNodeName
      *
-     * @return NodeInterface
+     * @throws UndefinedChildNode if the node does not have a child with the given name
      */
-    private static function childNode(ArrayNode $node, $childNodeName)
+    private static function childNode(ArrayNode $node, string $childNodeName): NodeInterface
     {
         if ($node instanceof PrototypedArrayNode && '*' === $childNodeName) {
-            return self::nodePrototypeProperty()->getValue($node);
+            return $node->getPrototype();
         }
 
         $children = self::nodeChildrenProperty()->getValue($node);
@@ -94,25 +87,11 @@ private static function childNode(ArrayNode $node, $childNodeName)
         return $children[$childNodeName];
     }
 
-    /**
-     * @return \ReflectionProperty
-     */
-    private static function nodeChildrenProperty()
+    private static function nodeChildrenProperty(): \ReflectionProperty
     {
         return self::$nodeChildrenProperty ??= new \ReflectionProperty(
             ArrayNode::class,
             'children'
         );
     }
-
-    /**
-     * @return \ReflectionProperty
-     */
-    private static function nodePrototypeProperty()
-    {
-        return self::$nodePrototypeProperty ??= new \ReflectionProperty(
-            PrototypedArrayNode::class,
-            'prototype'
-        );
-    }
 }
diff --git a/Partial/PartialProcessor.php b/Partial/PartialProcessor.php
index 3165642..399232f 100644
--- a/Partial/PartialProcessor.php
+++ b/Partial/PartialProcessor.php
@@ -8,15 +8,23 @@
 
 class PartialProcessor
 {
+    /**
+     * @param string|null $breadcrumbPath
+     *
+     * @return array
+     */
     public function process(ArrayNode $node, $breadcrumbPath, array $configs)
     {
         PartialNode::excludeEverythingNotInBreadcrumbPath($node, $breadcrumbPath);
 
-        $processor = new Processor();
-
-        return $processor->process($node, $configs);
+        return (new Processor())->process($node, $configs);
     }
 
+    /**
+     * @param string|null $breadcrumbPath
+     *
+     * @return array
+     */
     public function processConfiguration(ConfigurationInterface $configuration, $breadcrumbPath, array $configs)
     {
         return $this->process($configuration->getConfigTreeBuilder()->buildTree(), $breadcrumbPath, $configs);
diff --git a/PhpUnit/AbstractConfigurationConstraint.php b/PhpUnit/AbstractConfigurationConstraint.php
index be9c182..21fbf0e 100644
--- a/PhpUnit/AbstractConfigurationConstraint.php
+++ b/PhpUnit/AbstractConfigurationConstraint.php
@@ -8,22 +8,40 @@
 
 abstract class AbstractConfigurationConstraint extends Constraint
 {
+    /**
+     * @var ConfigurationInterface
+     */
     protected $configuration;
+
+    /**
+     * @var string|null
+     */
     protected $breadcrumbPath;
 
+    /**
+     * @param string|null $breadcrumbPath
+     */
     public function __construct(ConfigurationInterface $configuration, $breadcrumbPath = null)
     {
         $this->configuration = $configuration;
         $this->breadcrumbPath = $breadcrumbPath;
     }
 
+    /**
+     * @return array
+     */
     protected function processConfiguration(array $configurationValues)
     {
-        $processor = new PartialProcessor();
-
-        return $processor->processConfiguration($this->configuration, $this->breadcrumbPath, $configurationValues);
+        return (new PartialProcessor())->processConfiguration($this->configuration, $this->breadcrumbPath, $configurationValues);
     }
 
+    /**
+     * @param mixed $configurationValues
+     *
+     * @return void
+     *
+     * @throws \InvalidArgumentException if the configuration values structure is not the required shape
+     */
     protected function validateConfigurationValuesArray($configurationValues)
     {
         if (!is_array($configurationValues)) {
diff --git a/PhpUnit/ConfigurationTestCaseTrait.php b/PhpUnit/ConfigurationTestCaseTrait.php
index 98bbd19..fd260a8 100644
--- a/PhpUnit/ConfigurationTestCaseTrait.php
+++ b/PhpUnit/ConfigurationTestCaseTrait.php
@@ -3,10 +3,11 @@
 namespace Matthias\SymfonyConfigTest\PhpUnit;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\Config\Definition\ConfigurationInterface;
 
 /**
  * Add this trait to your Test Case to add the ability of testing your configuration
- * which should implement Symfony\Component\Config\Definition\ConfigurationInterface.
+ * which should implement {@see ConfigurationInterface}.
  */
 trait ConfigurationTestCaseTrait
 {
@@ -14,7 +15,7 @@ trait ConfigurationTestCaseTrait
      * Return the instance of ConfigurationInterface that should be used by the
      * Configuration-specific assertions in this test-case.
      *
-     * @return \Symfony\Component\Config\Definition\ConfigurationInterface
+     * @return ConfigurationInterface
      */
     abstract protected function getConfiguration();
 
@@ -29,6 +30,8 @@ abstract protected function getConfiguration();
      * @param array       $configurationValues
      * @param string|null $expectedMessage
      * @param bool        $useRegExp
+     *
+     * @return void
      */
     protected function assertConfigurationIsInvalid(array $configurationValues, $expectedMessage = null, $useRegExp = false)
     {
@@ -51,9 +54,11 @@ protected function assertConfigurationIsInvalid(array $configurationValues, $exp
      * to match the exception message using a regular expression.
      *
      * @param array       $configurationValues
-     * @param string      $breadcrumbPath      The path that should be validated, e.g. "doctrine.orm"
+     * @param string|null $breadcrumbPath      The path that should be validated, e.g. "doctrine.orm"
      * @param string|null $expectedMessage
      * @param bool        $useRegExp
+     *
+     * @return void
      */
     protected function assertPartialConfigurationIsInvalid(
         array $configurationValues,
@@ -79,6 +84,8 @@ protected function assertPartialConfigurationIsInvalid(
      *
      * @param array       $configurationValues
      * @param string|null $breadcrumbPath
+     *
+     * @return void
      */
     protected function assertConfigurationIsValid(array $configurationValues, $breadcrumbPath = null)
     {
@@ -99,6 +106,8 @@ protected function assertConfigurationIsValid(array $configurationValues, $bread
      * @param array       $configurationValues
      * @param array       $expectedProcessedConfiguration
      * @param string|null $breadcrumbPath
+     *
+     * @return void
      */
     protected function assertProcessedConfigurationEquals(
         array $configurationValues,
diff --git a/PhpUnit/ConfigurationValuesAreInvalidConstraint.php b/PhpUnit/ConfigurationValuesAreInvalidConstraint.php
index 849995e..02e7cde 100644
--- a/PhpUnit/ConfigurationValuesAreInvalidConstraint.php
+++ b/PhpUnit/ConfigurationValuesAreInvalidConstraint.php
@@ -2,6 +2,7 @@
 
 namespace Matthias\SymfonyConfigTest\PhpUnit;
 
+use PHPUnit\Framework\Constraint\Constraint;
 use PHPUnit\Framework\Constraint\ExceptionMessage;
 use PHPUnit\Framework\Constraint\ExceptionMessageIsOrContains;
 use PHPUnit\Framework\Constraint\ExceptionMessageMatchesRegularExpression;
@@ -13,9 +14,21 @@
 
 class ConfigurationValuesAreInvalidConstraint extends AbstractConfigurationConstraint
 {
+    /**
+     * @var string|null
+     */
     private $expectedMessage;
+
+    /**
+     * @var bool
+     */
     private $useRegExp;
 
+    /**
+     * @param string|null $expectedMessage
+     * @param bool        $useRegExp
+     * @param string|null $breadcrumbPath
+     */
     public function __construct(
         ConfigurationInterface $configuration,
         $expectedMessage = null,
@@ -28,6 +41,9 @@ public function __construct(
         $this->useRegExp = $useRegExp;
     }
 
+    /**
+     * {@inheritdoc}
+     */
     public function evaluate($other, $description = '', $returnResult = false): ?bool
     {
         $this->validateConfigurationValuesArray($other);
@@ -44,6 +60,7 @@ public function evaluate($other, $description = '', $returnResult = false): ?boo
 
         $this->fail($other, $description);
 
+        /** @phpstan-ignore deadCode.unreachable (legacy B/C layer) */
         return null;
     }
 
@@ -58,7 +75,7 @@ public function toString(): string
         return $toString;
     }
 
-    private function evaluateException(\Exception $exception, $description, $returnResult)
+    private function evaluateException(\Exception $exception, string $description = '', bool $returnResult = false): ?bool
     {
         if ($this->expectedMessage === null) {
             return true;
@@ -68,7 +85,7 @@ private function evaluateException(\Exception $exception, $description, $returnR
             ->evaluate($exception->getMessage(), $description, $returnResult);
     }
 
-    private function createPhpUnitConstraint()
+    private function createPhpUnitConstraint(): Constraint
     {
         if ($this->useRegExp) {
             // Available since PHPUnit 10.0.15
@@ -78,10 +95,12 @@ private function createPhpUnitConstraint()
 
             // Available between PHPUnit 10.0.0 and 10.0.14 (inclusive)
             if (class_exists(MessageMatchesRegularExpression::class)) {
+                /** @phpstan-ignore return.type (legacy B/C layer) */
                 return new MessageMatchesRegularExpression('exception', $this->expectedMessage);
             }
 
             // Available in PHPUnit 9.6
+            /** @phpstan-ignore class.notFound,return.type (legacy B/C layer) */
             return new ExceptionMessageRegularExpression($this->expectedMessage);
         }
 
@@ -92,10 +111,12 @@ private function createPhpUnitConstraint()
 
         // Available between PHPUnit 10.0.0 and 10.0.14 (inclusive)
         if (class_exists(MessageIsOrContains::class)) {
+            /** @phpstan-ignore return.type (legacy B/C layer) */
             return new MessageIsOrContains('exception', $this->expectedMessage);
         }
 
         // Available in PHPUnit 9.6
+        /** @phpstan-ignore class.notFound,return.type (legacy B/C layer) */
         return new ExceptionMessage($this->expectedMessage);
     }
 }
diff --git a/PhpUnit/ConfigurationValuesAreValidConstraint.php b/PhpUnit/ConfigurationValuesAreValidConstraint.php
index 13dbfd4..242a4c8 100644
--- a/PhpUnit/ConfigurationValuesAreValidConstraint.php
+++ b/PhpUnit/ConfigurationValuesAreValidConstraint.php
@@ -2,16 +2,10 @@
 
 namespace Matthias\SymfonyConfigTest\PhpUnit;
 
-use Symfony\Component\Config\Definition\ConfigurationInterface;
 use Symfony\Component\Config\Definition\Exception\InvalidConfigurationException;
 
 class ConfigurationValuesAreValidConstraint extends AbstractConfigurationConstraint
 {
-    public function __construct(ConfigurationInterface $configuration, $breadcrumbPath = null)
-    {
-        parent::__construct($configuration, $breadcrumbPath);
-    }
-
     public function evaluate($other, $description = '', $returnResult = false): ?bool
     {
         $this->validateConfigurationValuesArray($other);
diff --git a/PhpUnit/ProcessedConfigurationEqualsConstraint.php b/PhpUnit/ProcessedConfigurationEqualsConstraint.php
index 5fb5d22..f3b9f7e 100644
--- a/PhpUnit/ProcessedConfigurationEqualsConstraint.php
+++ b/PhpUnit/ProcessedConfigurationEqualsConstraint.php
@@ -7,8 +7,11 @@
 
 class ProcessedConfigurationEqualsConstraint extends AbstractConfigurationConstraint
 {
-    private $configurationValues;
+    private array $configurationValues;
 
+    /**
+     * @param string|null $breadcrumbPath
+     */
     public function __construct(
         ConfigurationInterface $configuration,
         array $configurationValues,
@@ -24,9 +27,7 @@ public function evaluate($other, $description = '', $returnResult = false): ?boo
     {
         $processedConfiguration = $this->processConfiguration($this->configurationValues);
 
-        $constraint = new IsEqual($other);
-
-        return $constraint->evaluate($processedConfiguration, '', $returnResult);
+        return (new IsEqual($other))->evaluate($processedConfiguration, '', $returnResult);
     }
 
     public function toString(): string
diff --git a/Tests/Partial/PartialNodeTest.php b/Tests/Partial/PartialNodeTest.php
index c0abc4d..8ef298c 100644
--- a/Tests/Partial/PartialNodeTest.php
+++ b/Tests/Partial/PartialNodeTest.php
@@ -30,8 +30,8 @@ public function it_strips_children_that_are_not_in_the_given_path_with_one_name(
                     ->children()
                         ->scalarNode('node_2_scalar_node');
 
+        /** @var ArrayNode $node */
         $node = $treeBuilder->buildTree();
-        /* @var ArrayNode $node */
 
         PartialNode::excludeEverythingNotInPath($node, ['node_2']);
 
@@ -65,8 +65,8 @@ public function it_strips_children_that_are_not_in_the_given_path_with_several_n
                     ->children()
                         ->scalarNode('scalar_node');
 
+        /** @var ArrayNode $node */
         $node = $treeBuilder->buildTree();
-        /* @var ArrayNode $node */
 
         PartialNode::excludeEverythingNotInPath($node, ['node_1', 'node_1_b']);
 
@@ -91,8 +91,8 @@ public function it_strips_children_when_leaf_node_is_not_an_array()
                 ->end()
                 ->scalarNode('node_3');
 
+        /** @var ArrayNode $node */
         $node = $treeBuilder->buildTree();
-        /* @var ArrayNode $node */
 
         PartialNode::excludeEverythingNotInPath($node, ['node_3']);
 
@@ -141,7 +141,13 @@ public function it_fails_when_a_requested_child_node_does_not_exist()
         $node = $treeBuilder->buildTree();
 
         $this->expectException(UndefinedChildNode::class);
-        $this->expectExceptionMessage('Undefined child node "non_existing_node" (the part of the path that was successful: "root.sub_node")');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('Undefined child node "non_existing_node" (the part of the path that was successful: "root.sub_node")');
+        } else {
+            $this->expectExceptionMessage('Undefined child node "non_existing_node" (the part of the path that was successful: "root.sub_node")');
+        }
 
         PartialNode::excludeEverythingNotInPath($node, ['sub_node', 'non_existing_node']);
     }
@@ -160,15 +166,20 @@ public function it_fails_when_a_requested_child_node_is_no_array_node_itself_and
         $node = $treeBuilder->buildTree();
 
         $this->expectException(ChildIsNotAnArrayNode::class);
-        $this->expectExceptionMessage('Child node "scalar_node" is not an array node (current path: "root.sub_node")');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('Child node "scalar_node" is not an array node (current path: "root.sub_node")');
+        } else {
+            $this->expectExceptionMessage('Child node "scalar_node" is not an array node (current path: "root.sub_node")');
+        }
 
         PartialNode::excludeEverythingNotInPath($node, ['sub_node', 'scalar_node', 'extra_node']);
     }
 
-    private function nodeOnlyHasChild(ArrayNode $node, $nodeName)
+    private function nodeOnlyHasChild(ArrayNode $node, string $nodeName)
     {
-        $property = new \ReflectionProperty($node, 'children');
-        $children = $property->getValue($node);
+        $children = (new \ReflectionProperty($node, 'children'))->getValue($node);
 
         $this->assertCount(1, $children);
         $firstChild = reset($children);
diff --git a/Tests/PhpUnit/ConfigurationTestCaseTraitTest.php b/Tests/PhpUnit/ConfigurationTestCaseTraitTest.php
index c5604e5..9f36b77 100644
--- a/Tests/PhpUnit/ConfigurationTestCaseTraitTest.php
+++ b/Tests/PhpUnit/ConfigurationTestCaseTraitTest.php
@@ -32,7 +32,13 @@ public function it_can_assert_that_a_configuration_is_invalid()
     public function it_fails_when_a_configuration_is_valid_when_it_should_have_been_invalid()
     {
         $this->expectException(ExpectationFailedException::class);
-        $this->expectExceptionMessage('invalid');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('invalid');
+        } else {
+            $this->expectExceptionMessage('invalid');
+        }
 
         $this->assertConfigurationIsInvalid(
             [
@@ -87,7 +93,13 @@ public function it_fails_when_a_processed_configuration_does_not_match_the_expec
         $value = 'some value';
 
         $this->expectException(ExpectationFailedException::class);
-        $this->expectExceptionMessage('equal');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('equal');
+        } else {
+            $this->expectExceptionMessage('equal');
+        }
 
         $this->assertProcessedConfigurationEquals(
             [
diff --git a/Tests/PhpUnit/ConfigurationValuesAreInvalidConstraintTest.php b/Tests/PhpUnit/ConfigurationValuesAreInvalidConstraintTest.php
index 5edce39..deefbf0 100644
--- a/Tests/PhpUnit/ConfigurationValuesAreInvalidConstraintTest.php
+++ b/Tests/PhpUnit/ConfigurationValuesAreInvalidConstraintTest.php
@@ -17,7 +17,13 @@ public function if_configuration_values_is_no_array_it_fails()
         $constraint = new ConfigurationValuesAreInvalidConstraint(new AlwaysValidConfiguration());
 
         $this->expectException(\InvalidArgumentException::class);
-        $this->expectExceptionMessage('array');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('array');
+        } else {
+            $this->expectExceptionMessage('array');
+        }
 
         $constraint->evaluate('not an array');
     }
@@ -28,7 +34,13 @@ public function if_configuration_values_is_no_array_of_arrays_it_fails()
         $constraint = new ConfigurationValuesAreInvalidConstraint(new AlwaysValidConfiguration());
 
         $this->expectException(\InvalidArgumentException::class);
-        $this->expectExceptionMessage('array');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('array');
+        } else {
+            $this->expectExceptionMessage('array');
+        }
 
         $constraint->evaluate(['not an array']);
     }
diff --git a/Tests/PhpUnit/ConfigurationValuesAreValidConstraintTest.php b/Tests/PhpUnit/ConfigurationValuesAreValidConstraintTest.php
index 946b38c..1ff5356 100644
--- a/Tests/PhpUnit/ConfigurationValuesAreValidConstraintTest.php
+++ b/Tests/PhpUnit/ConfigurationValuesAreValidConstraintTest.php
@@ -16,7 +16,13 @@ public function if_configuration_values_is_no_array_it_fails()
         $constraint = new ConfigurationValuesAreValidConstraint(new AlwaysValidConfiguration());
 
         $this->expectException(\InvalidArgumentException::class);
-        $this->expectExceptionMessage('array');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('array');
+        } else {
+            $this->expectExceptionMessage('array');
+        }
 
         $constraint->evaluate('not an array');
     }
@@ -27,7 +33,13 @@ public function if_configuration_values_is_no_array_of_arrays_it_fails()
         $constraint = new ConfigurationValuesAreValidConstraint(new AlwaysValidConfiguration());
 
         $this->expectException(\InvalidArgumentException::class);
-        $this->expectExceptionMessage('array');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('array');
+        } else {
+            $this->expectExceptionMessage('array');
+        }
 
         $constraint->evaluate(['not an array']);
     }
diff --git a/Tests/PhpUnit/PartialConfigurationIntegrationTest.php b/Tests/PhpUnit/PartialConfigurationIntegrationTest.php
index cbdcd5c..9d9a44b 100644
--- a/Tests/PhpUnit/PartialConfigurationIntegrationTest.php
+++ b/Tests/PhpUnit/PartialConfigurationIntegrationTest.php
@@ -33,7 +33,13 @@ public function it_can_assert_that_a_configuration_is_invalid()
     public function it_fails_when_a_configuration_is_valid_when_it_should_have_been_invalid()
     {
         $this->expectException(ExpectationFailedException::class);
-        $this->expectExceptionMessage('invalid');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('invalid');
+        } else {
+            $this->expectExceptionMessage('invalid');
+        }
 
         $this->assertPartialConfigurationIsInvalid(
             [
@@ -66,7 +72,13 @@ public function it_can_assert_that_a_configuration_is_valid()
     public function it_fails_when_a_configuration_is_invalid_when_it_should_have_been_valid()
     {
         $this->expectException(ExpectationFailedException::class);
-        $this->expectExceptionMessage('valid');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('valid');
+        } else {
+            $this->expectExceptionMessage('valid');
+        }
 
         $this->assertConfigurationIsValid(
             [
@@ -106,7 +118,14 @@ public function it_fails_when_a_processed_configuration_does_not_match_the_expec
         $value = 'some value';
 
         $this->expectException(ExpectationFailedException::class);
-        $this->expectExceptionMessage('equal');
+
+        /** @phpstan-ignore function.alreadyNarrowedType (compat layer for PHPUnit 13.2 deprecations) */
+        if (method_exists($this, 'expectExceptionMessageIsOrContains')) {
+            $this->expectExceptionMessageIsOrContains('equal');
+        } else {
+            $this->expectExceptionMessage('equal');
+        }
+
         $this->assertProcessedConfigurationEquals(
             [
                 [
diff --git a/composer.json b/composer.json
index 581bf56..e1e3c29 100644
--- a/composer.json
+++ b/composer.json
@@ -17,6 +17,11 @@
         "phpunit/phpunit": "^10.5 || ^11.0 || ^12.0 || ^13.0",
         "symfony/config": "^5.4 || ^6.4 || ^7.0 || ^8.0"
     },
+    "require-dev": {
+        "phpstan/extension-installer": "^1.4.3",
+        "phpstan/phpstan": "2.2.14",
+        "phpstan/phpstan-phpunit": "2.0.18"
+    },
     "autoload": {
         "psr-4" : { "Matthias\\SymfonyConfigTest\\" : "" },
         "exclude-from-classmap": ["/Tests/"]
@@ -24,6 +29,11 @@
     "autoload-dev": {
         "psr-4" : { "Matthias\\SymfonyConfigTest\\Tests\\" : "Tests/" }
     },
+    "config": {
+        "allow-plugins": {
+            "phpstan/extension-installer": true
+        }
+    },
     "extra": {
         "branch-alias": {
             "dev-master": "6.x-dev"
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..55beb38
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,6 @@
+parameters:
+  level: 4
+  paths:
+    - %currentWorkingDirectory%/Partial
+    - %currentWorkingDirectory%/PhpUnit
+    - %currentWorkingDirectory%/Tests