diff --git a/src/Proxy/ProxyGenerator.php b/src/Proxy/ProxyGenerator.php
index ec6fb1004..9f35fd5a2 100644
--- a/src/Proxy/ProxyGenerator.php
+++ b/src/Proxy/ProxyGenerator.php
@@ -1282,7 +1282,6 @@ function (ReflectionType $intersectedType) use ($method, $parameter) {
         if (
             $type->allowsNull()
             && ! in_array($name, ['mixed', 'null'], true)
-            && ($parameter === null || ! $parameter->isDefaultValueAvailable() || $parameter->getDefaultValue() !== null)
         ) {
             $name = '?' . $name;
         }
diff --git a/tests/Common/Proxy/Php8UnionTypes.php b/tests/Common/Proxy/Php8UnionTypes.php
index ab5c391c8..c95412746 100644
--- a/tests/Common/Proxy/Php8UnionTypes.php
+++ b/tests/Common/Proxy/Php8UnionTypes.php
@@ -12,10 +12,16 @@ class Php8UnionTypes
 
     public function setValue(stdClass|array $value) : bool|float
     {
+        return true;
     }
 
     public function setNullableValue(stdClass|array|null $value) : bool|float|null
     {
+        return true;
     }
 
+    public function setNullableValueDefaultNull(stdClass|array|null $value = null) : bool|float|null
+    {
+        return true;
+    }
 }
diff --git a/tests/Common/Proxy/ProxyGeneratorTest.php b/tests/Common/Proxy/ProxyGeneratorTest.php
index 59c1eb3ef..59b796eda 100644
--- a/tests/Common/Proxy/ProxyGeneratorTest.php
+++ b/tests/Common/Proxy/ProxyGeneratorTest.php
@@ -180,7 +180,7 @@ public function testClassWithScalarTypeHintsOnProxiedMethods()
         self::assertEquals(1, substr_count($classCode, 'function combinationOfTypeHintsAndNormal(\stdClass $a, \Countable $b, $c, int $d)'));
         self::assertEquals(1, substr_count($classCode, 'function typeHintsWithVariadic(int ...$foo)'));
         self::assertEquals(1, substr_count($classCode, 'function withDefaultValue(int $foo = 123)'));
-        self::assertEquals(1, substr_count($classCode, 'function withDefaultValueNull(int $foo = NULL)'));
+        self::assertEquals(1, substr_count($classCode, 'function withDefaultValueNull(?int $foo = NULL)'));
     }
 
     public function testClassWithReturnTypesOnProxiedMethods()
@@ -220,8 +220,8 @@ public function testClassWithNullableTypeHintsOnProxiedMethods()
         self::assertEquals(1, substr_count($classCode, 'function nullableTypeHintObject(?\stdClass $param)'));
         self::assertEquals(1, substr_count($classCode, 'function nullableTypeHintSelf(?\\' . $className . ' $param)'));
         self::assertEquals(1, substr_count($classCode, 'function nullableTypeHintWithDefault(?int $param = 123)'));
-        self::assertEquals(1, substr_count($classCode, 'function nullableTypeHintWithDefaultNull(int $param = NULL)'));
-        self::assertEquals(1, substr_count($classCode, 'function notNullableTypeHintWithDefaultNull(int $param = NULL)'));
+        self::assertEquals(1, substr_count($classCode, 'function nullableTypeHintWithDefaultNull(?int $param = NULL)'));
+        self::assertEquals(1, substr_count($classCode, 'function notNullableTypeHintWithDefaultNull(?int $param = NULL)'));
     }
 
     public function testClassWithNullableReturnTypesOnProxiedMethods()
@@ -460,6 +460,11 @@ public function testPhp8UnionTypes()
             'setNullableValue(\stdClass|array|null $value): float|bool|null',
             file_get_contents(__DIR__ . '/generated/__CG__DoctrineTestsCommonProxyPhp8UnionTypes.php')
         );
+
+        self::assertStringContainsString(
+            'setNullableValueDefaultNull(\stdClass|array|null $value = NULL): float|bool|null',
+            file_get_contents(__DIR__ . '/generated/__CG__DoctrineTestsCommonProxyPhp8UnionTypes.php')
+        );
     }
 
     /**