diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 70f1073..426f1f5 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -30,4 +30,4 @@ jobs:
       os: >-
         ['ubuntu-latest', 'windows-latest']
       php: >-
-        ['8.1', '8.2', '8.3']
+        ['8.1', '8.2', '8.3', '8.4']
diff --git a/.github/workflows/composer-require-checker.yml b/.github/workflows/composer-require-checker.yml
index 822591f..919a073 100644
--- a/.github/workflows/composer-require-checker.yml
+++ b/.github/workflows/composer-require-checker.yml
@@ -32,4 +32,4 @@ jobs:
       os: >-
         ['ubuntu-latest']
       php: >-
-        ['8.1', '8.2', '8.3']
+        ['8.1', '8.2', '8.3', '8.4']
diff --git a/.github/workflows/mutation.yml b/.github/workflows/mutation.yml
index dc464eb..7a54fcc 100644
--- a/.github/workflows/mutation.yml
+++ b/.github/workflows/mutation.yml
@@ -29,6 +29,6 @@ jobs:
       os: >-
         ['ubuntu-latest']
       php: >-
-        ['8.3']
+        ['8.4']
     secrets:
       STRYKER_DASHBOARD_API_KEY: ${{ secrets.STRYKER_DASHBOARD_API_KEY }}
diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
index 873eeb5..9e12684 100644
--- a/.github/workflows/static.yml
+++ b/.github/workflows/static.yml
@@ -30,4 +30,4 @@ jobs:
       os: >-
         ['ubuntu-latest']
       php: >-
-        ['8.1', '8.2', '8.3']
+        ['8.1', '8.2', '8.3', '8.4']
diff --git a/.github/workflows/yiisoft-di.yml b/.github/workflows/yiisoft-di.yml
index 5f1bdfb..5285df3 100644
--- a/.github/workflows/yiisoft-di.yml
+++ b/.github/workflows/yiisoft-di.yml
@@ -37,6 +37,7 @@ jobs:
           - "8.1"
           - "8.2"
           - "8.3"
+          - "8.4"
 
     steps:
       - name: Checkout Yii Definitions
diff --git a/.github/workflows/yiisoft-factory.yml b/.github/workflows/yiisoft-factory.yml
index 5a0b40c..f75fff3 100644
--- a/.github/workflows/yiisoft-factory.yml
+++ b/.github/workflows/yiisoft-factory.yml
@@ -37,6 +37,7 @@ jobs:
           - "8.1"
           - "8.2"
           - "8.3"
+          - "8.4"
 
     steps:
       - name: Checkout Yii Definitions
diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
index 43dd8b5..5c4e99a 100644
--- a/.php-cs-fixer.dist.php
+++ b/.php-cs-fixer.dist.php
@@ -6,10 +6,12 @@
 use PhpCsFixer\Finder;
 use PhpCsFixer\Runner\Parallel\ParallelConfigFactory;
 
-$finder = (new Finder())->in([
-    __DIR__ . '/src',
-    __DIR__ . '/tests',
-]);
+$finder = (new Finder())
+    ->in([
+        __DIR__ . '/src',
+        __DIR__ . '/tests',
+    ])
+    ->exclude('Php8_4/');
 
 return (new Config())
     ->setParallelConfig(ParallelConfigFactory::detect())
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f35b51b..a71038c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,9 +2,12 @@
 
 ## 3.3.2 under development
 
+- Chg #105: Change PHP constraint in `composer.json` to `~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0` (@vjik)
 - Chg #106: Bump minimal required PHP version to 8.1 (@vjik)
 - Enh #106: Minor performance optimization: use FQN for PHP functions, remove unnecessary conditions (@vjik)
 - Enh #106: Mark readonly properties (@vjik)
+- Bug #105: Explicitly mark nullable parameters (@vjik)
+- Enh #105: Improve definition validation for readonly properties and properties with asymmetric visibility (@vjik)
 
 ## 3.3.1 December 16, 2024
 
diff --git a/composer.json b/composer.json
index 33fc9cf..276b7ad 100644
--- a/composer.json
+++ b/composer.json
@@ -26,7 +26,7 @@
         }
     ],
     "require": {
-        "php": "^8.1",
+        "php": "~8.1.0 || ~8.2.0 || ~8.3.0 || ~8.4.0",
         "psr/container": "^1.0 || ^2.0"
     },
     "require-dev": {
@@ -37,7 +37,7 @@
         "roave/infection-static-analysis-plugin": "^1.35",
         "spatie/phpunit-watcher": "^1.24",
         "vimeo/psalm": "^5.26.1 || ^6.7.1",
-        "yiisoft/test-support": "^3.0"
+        "yiisoft/test-support": "^3.0.1"
     },
     "autoload": {
         "psr-4": {
@@ -58,7 +58,7 @@
         }
     },
     "scripts": {
-        "php-cs-fixer": "php-cs-fixer fix",
+        "php-cs-fixer": "PHP_CS_FIXER_IGNORE_ENV=1 php-cs-fixer fix",
         "rector": "rector",
         "test": "phpunit --testdox --no-interaction",
         "test-watch": "phpunit-watcher watch"
diff --git a/infection.json.dist b/infection.json.dist
index 3776e22..2185614 100644
--- a/infection.json.dist
+++ b/infection.json.dist
@@ -11,6 +11,11 @@
         }
     },
     "mutators": {
-        "@default": true
+        "@default": true,
+        "LessThan": {
+            "ignoreSourceCodeByRegex": [
+                ".*\\(PHP_VERSION_ID .*"
+            ]
+        }
     }
 }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index c21dbf0..00bbbd3 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -21,6 +21,7 @@
         <testsuite name="Yii Definitions tests">
             <directory>./tests/Unit</directory>
             <directory phpVersion="8.2" phpVersionOperator=">=">./tests/Php8_2</directory>
+            <directory phpVersion="8.4" phpVersionOperator=">=">./tests/Php8_4</directory>
         </testsuite>
     </testsuites>
 
diff --git a/src/Exception/NotInstantiableClassException.php b/src/Exception/NotInstantiableClassException.php
index 16250af..eb1b1dc 100644
--- a/src/Exception/NotInstantiableClassException.php
+++ b/src/Exception/NotInstantiableClassException.php
@@ -11,7 +11,7 @@
  */
 final class NotInstantiableClassException extends NotInstantiableException
 {
-    public function __construct(string $class, string $message = null, int $code = 0, Exception $previous = null)
+    public function __construct(string $class, ?string $message = null, int $code = 0, ?Exception $previous = null)
     {
         if ($message === null) {
             $message = "Can not instantiate $class.";
diff --git a/src/Helpers/DefinitionValidator.php b/src/Helpers/DefinitionValidator.php
index 05ca170..110732e 100644
--- a/src/Helpers/DefinitionValidator.php
+++ b/src/Helpers/DefinitionValidator.php
@@ -6,11 +6,13 @@
 
 use ReflectionClass;
 use ReflectionException;
+use ReflectionProperty;
 use Yiisoft\Definitions\ArrayDefinition;
 use Yiisoft\Definitions\Contract\DefinitionInterface;
 use Yiisoft\Definitions\Contract\ReferenceInterface;
 use Yiisoft\Definitions\Exception\InvalidConfigException;
 
+use function count;
 use function in_array;
 use function is_array;
 use function is_callable;
@@ -85,7 +87,7 @@ public static function validateArrayDefinition(array $definition, ?string $id =
         }
         $classPublicProperties = [];
         foreach ($classReflection->getProperties() as $reflectionProperty) {
-            if ($reflectionProperty->isPublic()) {
+            if (self::isPublicWritableProperty($reflectionProperty)) {
                 $classPublicProperties[] = $reflectionProperty->getName();
             }
         }
@@ -261,7 +263,7 @@ private static function validateProperty(
         } elseif (!in_array($parsedKey, $classPublicProperties, true)) {
             throw new InvalidConfigException(
                 sprintf(
-                    'Invalid definition: property "%s" must be public.',
+                    'Invalid definition: property "%s" must be public and writable.',
                     $className . '::' . $key,
                 ),
             );
@@ -327,4 +329,26 @@ private static function validateString(mixed $class): void
             throw new InvalidConfigException('Invalid definition: class name must be a non-empty string.');
         }
     }
+
+    private static function isPublicWritableProperty(ReflectionProperty $property): bool
+    {
+        if (!$property->isPublic()) {
+            return false;
+        }
+
+        if ($property->isReadOnly()) {
+            return false;
+        }
+
+        if (PHP_VERSION_ID < 80400) {
+            return true;
+        }
+
+        $modifiers = $property->getModifiers();
+
+        /**
+         * @psalm-suppress UndefinedConstant, MixedOperand Needs for PHP 8.3 or lower
+         */
+        return ($modifiers & (ReflectionProperty::IS_PRIVATE_SET | ReflectionProperty::IS_PROTECTED_SET)) === 0;
+    }
 }
diff --git a/src/ParameterDefinition.php b/src/ParameterDefinition.php
index 0fbe51c..34fff5a 100644
--- a/src/ParameterDefinition.php
+++ b/src/ParameterDefinition.php
@@ -216,10 +216,7 @@ private function getCallable(): string
         if ($class !== null) {
             $callable[] = $class->getName();
         }
-        $callable[] = $this->parameter
-                ->getDeclaringFunction()
-                ->getName() .
-            '()';
+        $callable[] = $this->parameter->getDeclaringFunction()->getName() . '()';
 
         return implode('::', $callable);
     }
diff --git a/tests/Php8_2/ParameterDefinitionTest.php b/tests/Php8_2/ParameterDefinitionTest.php
index 75caf79..9d57783 100644
--- a/tests/Php8_2/ParameterDefinitionTest.php
+++ b/tests/Php8_2/ParameterDefinitionTest.php
@@ -22,7 +22,7 @@ public function testResolveUnionTypeWithIntersectionType(): void
         ]);
 
         $definition = new ParameterDefinition(
-            $this->getFirstParameter(fn (Bike|(GearBox&stdClass)|Chair $class) => true)
+            $this->getFirstParameter(fn(Bike|(GearBox&stdClass)|Chair $class) => true),
         );
 
         $result = $definition->resolve($container);
diff --git a/tests/Php8_4/AsymmetricVisibility/DefinitionValidatorTest.php b/tests/Php8_4/AsymmetricVisibility/DefinitionValidatorTest.php
new file mode 100644
index 0000000..dfed394
--- /dev/null
+++ b/tests/Php8_4/AsymmetricVisibility/DefinitionValidatorTest.php
@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Definitions\Tests\Php8_4\AsymmetricVisibility;
+
+use PHPUnit\Framework\TestCase;
+use Yiisoft\Definitions\Exception\InvalidConfigException;
+use Yiisoft\Definitions\Helpers\DefinitionValidator;
+
+final class DefinitionValidatorTest extends TestCase
+{
+    public function testPrivateSet(): void
+    {
+        $definition = [
+            'class' => PublicGet::class,
+            '$privateVar' => 'test',
+        ];
+
+        $this->expectException(InvalidConfigException::class);
+        $this->expectExceptionMessage(
+            'Invalid definition: property "Yiisoft\Definitions\Tests\Php8_4\AsymmetricVisibility\PublicGet::$privateVar" must be public and writable.',
+        );
+        DefinitionValidator::validate($definition);
+    }
+
+    public function testProtectedSet(): void
+    {
+        $definition = [
+            'class' => PublicGet::class,
+            '$protectedVar' => 'test',
+        ];
+
+        $this->expectException(InvalidConfigException::class);
+        $this->expectExceptionMessage(
+            'Invalid definition: property "Yiisoft\Definitions\Tests\Php8_4\AsymmetricVisibility\PublicGet::$protectedVar" must be public and writable.',
+        );
+        DefinitionValidator::validate($definition);
+    }
+}
diff --git a/tests/Php8_4/AsymmetricVisibility/PublicGet.php b/tests/Php8_4/AsymmetricVisibility/PublicGet.php
new file mode 100644
index 0000000..ffbfaef
--- /dev/null
+++ b/tests/Php8_4/AsymmetricVisibility/PublicGet.php
@@ -0,0 +1,11 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Definitions\Tests\Php8_4\AsymmetricVisibility;
+
+final class PublicGet
+{
+    public private(set) string $privateVar = '';
+    public protected(set) string $protectedVar = '';
+}
diff --git a/tests/Support/OptionalConcreteDependency.php b/tests/Support/OptionalConcreteDependency.php
deleted file mode 100644
index cc144bf..0000000
--- a/tests/Support/OptionalConcreteDependency.php
+++ /dev/null
@@ -1,10 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Yiisoft\Definitions\Tests\Support;
-
-final class OptionalConcreteDependency
-{
-    public function __construct(Car $car = null) {}
-}
diff --git a/tests/Support/OptionalInterfaceDependency.php b/tests/Support/OptionalInterfaceDependency.php
deleted file mode 100644
index f50d5af..0000000
--- a/tests/Support/OptionalInterfaceDependency.php
+++ /dev/null
@@ -1,10 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Yiisoft\Definitions\Tests\Support;
-
-final class OptionalInterfaceDependency
-{
-    public function __construct(EngineInterface $engine = null) {}
-}
diff --git a/tests/Support/ReadonlyProperty.php b/tests/Support/ReadonlyProperty.php
new file mode 100644
index 0000000..b547447
--- /dev/null
+++ b/tests/Support/ReadonlyProperty.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Definitions\Tests\Support;
+
+final class ReadonlyProperty
+{
+    public readonly string $var;
+}
diff --git a/tests/Support/UnionTypeWithIntersectionTypeDependency.php b/tests/Support/UnionTypeWithIntersectionTypeDependency.php
index 46cb22e..b248dcb 100644
--- a/tests/Support/UnionTypeWithIntersectionTypeDependency.php
+++ b/tests/Support/UnionTypeWithIntersectionTypeDependency.php
@@ -7,7 +7,6 @@
 final class UnionTypeWithIntersectionTypeDependency
 {
     public function __construct(
-        public Bike|(GearBox&stdClass)|Chair $dependency
-    ) {
-    }
+        public Bike|(GearBox&stdClass)|Chair $dependency,
+    ) {}
 }
diff --git a/tests/Unit/Helpers/DefinitionExtractorTest.php b/tests/Unit/Helpers/DefinitionExtractorTest.php
index 35e33a8..0da742f 100644
--- a/tests/Unit/Helpers/DefinitionExtractorTest.php
+++ b/tests/Unit/Helpers/DefinitionExtractorTest.php
@@ -20,8 +20,6 @@
 use Yiisoft\Definitions\Tests\Support\GearBox;
 use Yiisoft\Definitions\Tests\Support\NullableConcreteDependency;
 use Yiisoft\Definitions\Tests\Support\NullableInterfaceDependency;
-use Yiisoft\Definitions\Tests\Support\OptionalConcreteDependency;
-use Yiisoft\Definitions\Tests\Support\OptionalInterfaceDependency;
 use Yiisoft\Definitions\Tests\Support\NullableOptionalConcreteDependency;
 use Yiisoft\Definitions\Tests\Support\NullableOptionalInterfaceDependency;
 use Yiisoft\Definitions\Tests\Support\RedChair;
@@ -102,15 +100,6 @@ public function testResolveGearBoxConstructor(): void
         $this->assertEquals(5, $dependencies['maxGear']->resolve($container));
     }
 
-    public function testOptionalInterfaceDependency(): void
-    {
-        $container = new SimpleContainer();
-        /** @var DefinitionInterface[] $dependencies */
-        $dependencies = DefinitionExtractor::fromClassName(OptionalInterfaceDependency::class);
-        $this->assertCount(1, $dependencies);
-        $this->assertEquals(null, $dependencies['engine']->resolve($container));
-    }
-
     public function testNullableInterfaceDependency(): void
     {
         $container = new SimpleContainer();
@@ -121,15 +110,6 @@ public function testNullableInterfaceDependency(): void
         $dependencies['engine']->resolve($container);
     }
 
-    public function testOptionalConcreteDependency(): void
-    {
-        $container = new SimpleContainer();
-        /** @var DefinitionInterface[] $dependencies */
-        $dependencies = DefinitionExtractor::fromClassName(OptionalConcreteDependency::class);
-        $this->assertCount(1, $dependencies);
-        $this->assertEquals(null, $dependencies['car']->resolve($container));
-    }
-
     public function testNullableConcreteDependency(): void
     {
         $container = new SimpleContainer();
@@ -152,7 +132,6 @@ public function testNullableOptionalConcreteDependency(): void
     public function testNullableOptionalInterfaceDependency(): void
     {
         $container = new SimpleContainer();
-        /** @var DefinitionInterface[] $dependencies */
         $dependencies = DefinitionExtractor::fromClassName(NullableOptionalInterfaceDependency::class);
         $this->assertCount(1, $dependencies);
         $this->assertEquals(null, $dependencies['engine']->resolve($container));
diff --git a/tests/Unit/Helpers/DefinitionValidatorTest.php b/tests/Unit/Helpers/DefinitionValidatorTest.php
index 43c3e4d..108e709 100644
--- a/tests/Unit/Helpers/DefinitionValidatorTest.php
+++ b/tests/Unit/Helpers/DefinitionValidatorTest.php
@@ -17,6 +17,7 @@
 use Yiisoft\Definitions\Tests\Support\GearBox;
 use Yiisoft\Definitions\Tests\Support\MagicCall;
 use Yiisoft\Definitions\Tests\Support\Phone;
+use Yiisoft\Definitions\Tests\Support\ReadonlyProperty;
 use Yiisoft\Definitions\Tests\Support\Recorder;
 use Yiisoft\Definitions\Tests\Support\UTF8User;
 use Yiisoft\Definitions\ValueDefinition;
@@ -73,7 +74,7 @@ public static function dataInvalidProperty(): array
                 $object1::class,
                 '$invisible',
                 sprintf(
-                    'Invalid definition: property "%s" must be public.',
+                    'Invalid definition: property "%s" must be public and writable.',
                     $object1::class . '::$invisible',
                 ),
             ],
@@ -81,7 +82,7 @@ public static function dataInvalidProperty(): array
                 UTF8User::class,
                 '$имя',
                 sprintf(
-                    'Invalid definition: property "%s" must be public.',
+                    'Invalid definition: property "%s" must be public and writable.',
                     UTF8User::class . '::$имя',
                 ),
             ],
@@ -367,4 +368,18 @@ public function testIncorrectMethodName(array $config, string $message): void
         $this->expectExceptionMessage($message);
         DefinitionValidator::validate($config);
     }
+
+    public function testReadonlyProperty(): void
+    {
+        $definition = [
+            'class' => ReadonlyProperty::class,
+            '$var' => 'test',
+        ];
+
+        $this->expectException(InvalidConfigException::class);
+        $this->expectExceptionMessage(
+            'Invalid definition: property "Yiisoft\Definitions\Tests\Support\ReadonlyProperty::$var" must be public and writable.',
+        );
+        DefinitionValidator::validate($definition);
+    }
 }
diff --git a/tests/Unit/ParameterDefinitionTest.php b/tests/Unit/ParameterDefinitionTest.php
index 239c15f..8357994 100644
--- a/tests/Unit/ParameterDefinitionTest.php
+++ b/tests/Unit/ParameterDefinitionTest.php
@@ -13,6 +13,7 @@
 use ReflectionParameter;
 use RuntimeException;
 use stdClass;
+use Throwable;
 use Yiisoft\Definitions\Exception\InvalidConfigException;
 use Yiisoft\Definitions\Exception\NotInstantiableException;
 use Yiisoft\Definitions\ParameterDefinition;
@@ -84,7 +85,7 @@ public static function dataHasValue(): array
             static fn(
                 string $a,
                 ?string $b,
-                string $c = null,
+                ?string $c = null,
                 string $d = 'hello',
             ): bool => true,
         );
@@ -138,10 +139,6 @@ public static function dataResolve(): array
                 7,
                 self::getFirstParameter(static fn(int $n = 7) => true),
             ],
-            'defaultNull' => [
-                null,
-                self::getFirstParameter(static fn(int $n = null) => true),
-            ],
             'nullableAndDefaultNull' => [
                 null,
                 self::getFirstParameter(static fn(?int $n = null) => true),
@@ -167,13 +164,21 @@ public function testResolveNonTypedParameter(): void
         );
         $container = new SimpleContainer();
 
-        $this->expectException(NotInstantiableException::class);
-        $this->expectExceptionMessage(
-            'Can not determine value of the "x" parameter without type when instantiating '
-            . '"Yiisoft\Definitions\Tests\Unit\ParameterDefinitionTest::Yiisoft\Definitions\Tests\Unit\{closure}()"'
-            . '. Please specify argument explicitly.',
+        $exception = null;
+        try {
+            $definition->resolve($container);
+        } catch (Throwable $exception) {
+        }
+
+        $this->assertInstanceOf(NotInstantiableException::class, $exception);
+        $this->assertStringStartsWith(
+            'Can not determine value of the "x" parameter without type when instantiating "Yiisoft\Definitions\Tests\Unit\ParameterDefinitionTest::',
+            $exception->getMessage(),
+        );
+        $this->assertStringEndsWith(
+            'Please specify argument explicitly.',
+            $exception->getMessage(),
         );
-        $definition->resolve($container);
     }
 
     public function testResolveBuiltinParameter(): void
@@ -185,13 +190,21 @@ public function testResolveBuiltinParameter(): void
         );
         $container = new SimpleContainer();
 
-        $this->expectException(NotInstantiableException::class);
-        $this->expectExceptionMessage(
-            'Can not determine value of the "n" parameter of type "int" when instantiating '
-            . '"Yiisoft\Definitions\Tests\Unit\ParameterDefinitionTest::Yiisoft\Definitions\Tests\Unit\{closure}()".'
-            . ' Please specify argument explicitly.',
+        $exception = null;
+        try {
+            $definition->resolve($container);
+        } catch (Throwable $exception) {
+        }
+
+        $this->assertInstanceOf(NotInstantiableException::class, $exception);
+        $this->assertStringStartsWith(
+            'Can not determine value of the "n" parameter of type "int" when instantiating "Yiisoft\Definitions\Tests\Unit\ParameterDefinitionTest::',
+            $exception->getMessage(),
+        );
+        $this->assertStringEndsWith(
+            'Please specify argument explicitly.',
+            $exception->getMessage(),
         );
-        $definition->resolve($container);
     }
 
     public function testResolveSelf(): void
@@ -420,9 +433,18 @@ public function testNotResolveIntersectionType(): void
             self::getFirstParameter(fn(GearBox&stdClass $class) => true),
         );
 
-        $this->expectException(NotInstantiableException::class);
-        $this->expectExceptionMessage('Can not determine value of the "class" parameter of type ');
-        $definition->resolve($container);
+        $exception = null;
+        try {
+            $definition->resolve($container);
+        } catch (Throwable $exception) {
+        }
+
+        $this->assertInstanceOf(NotInstantiableException::class, $exception);
+        $this->assertStringStartsWith(
+            'Can not determine value of the "class" parameter of type "Yiisoft\Definitions\Tests\Support\GearBox&stdClass" when instantiating "Yiisoft\Definitions\Tests\Unit\ParameterDefinitionTest::',
+            $exception->getMessage(),
+        );
+        $this->assertStringEndsWith('}()". Please specify argument explicitly.', $exception->getMessage());
     }
 
     /**