diff --git a/.github/workflows/run_on_project.yaml b/.github/workflows/run_on_project.yaml
index 941cd8a2..b9c25ed2 100644
--- a/.github/workflows/run_on_project.yaml
+++ b/.github/workflows/run_on_project.yaml
@@ -13,7 +13,7 @@ jobs:
         strategy:
             fail-fast: false
             matrix:
-                php_version: ['8.2']
+                php_version: ['8.4']
 
         steps:
             -
@@ -24,7 +24,7 @@ jobs:
 
             -   run: composer require rector/argtyper --ansi
 
-            # clone laravel project with dependencies
+            # clone symfony/console project with dependencies
             -   run: git clone https://github.com/symfony/console.git --depth=1
             -   run: composer install --working-dir console --ansi
 
diff --git a/src/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector.php b/src/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector.php
index 0a259cb2..28a79e90 100644
--- a/src/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector.php
+++ b/src/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector.php
@@ -91,11 +91,11 @@ public function refactor(Node $node): ?Class_
                     continue;
                 }
 
-                // keep nullability if the param is already nullable or implicitly nullable via a null default,
-                // otherwise the "?" would be dropped and the param would become implicitly nullable (deprecated)
+                // a null default value implies the type must stay nullable
                 $isNullable = $classMethodType->isNullable()
                     || $param->type instanceof NullableType
                     || $this->hasNullDefault($param);
+
                 $typeNode = TypeResolver::resolveTypeNode($classMethodType->getType());
 
                 if ($this->shouldSkipOverride($param, $classMethodType)) {
diff --git a/src/Rector/Rector/Function_/AddFunctionParamTypeRector.php b/src/Rector/Rector/Function_/AddFunctionParamTypeRector.php
index 7db7c8c7..b58277e5 100644
--- a/src/Rector/Rector/Function_/AddFunctionParamTypeRector.php
+++ b/src/Rector/Rector/Function_/AddFunctionParamTypeRector.php
@@ -5,8 +5,10 @@
 namespace Rector\ArgTyper\Rector\Rector\Function_;
 
 use PhpParser\Node;
+use PhpParser\Node\Expr\ConstFetch;
 use PhpParser\Node\Name;
 use PhpParser\Node\NullableType;
+use PhpParser\Node\Param;
 use PhpParser\Node\Stmt\Function_;
 use PHPStan\Type\NeverType;
 use PHPStan\Type\NullType;
@@ -64,7 +66,8 @@ public function refactor(Node $node): ?Function_
                 continue;
             }
 
-            $isNullable = $paramFunctionType->isNullable();
+            // a null default value implies the type must stay nullable
+            $isNullable = $paramFunctionType->isNullable() || $this->hasDefaultNull($param);
             $typeNode = TypeResolver::resolveTypeNode($paramFunctionType->getType());
 
             if ($paramFunctionType->isObjectType() && ($param->type instanceof Name || ($param->type instanceof NullableType && $param->type->type instanceof Name))) {
@@ -87,4 +90,13 @@ public function refactor(Node $node): ?Function_
 
         return $node;
     }
+
+    private function hasDefaultNull(Param $param): bool
+    {
+        if (! $param->default instanceof ConstFetch) {
+            return false;
+        }
+
+        return $param->default->name->toLowerString() === 'null';
+    }
 }
diff --git a/tests/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector/AddClassMethodParamTypeRectorTest.php b/tests/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector/AddClassMethodParamTypeRectorTest.php
index d637a5e6..1dfaa04f 100644
--- a/tests/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector/AddClassMethodParamTypeRectorTest.php
+++ b/tests/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector/AddClassMethodParamTypeRectorTest.php
@@ -10,6 +10,7 @@
 use PHPUnit\Framework\Attributes\DataProvider;
 use Rector\ArgTyper\Configuration\CallLikeTypesConfigurationProvider;
 use Rector\ArgTyper\Rector\ValueObject\ClassMethodType;
+use Rector\ArgTyper\Tests\Rector\Rector\ClassMethod\AddClassMethodParamTypeRector\Fixture\AddNullableForDefaultNull;
 use Rector\ArgTyper\Tests\Rector\Rector\ClassMethod\AddClassMethodParamTypeRector\Fixture\AddNullableScalarFromNullDefault;
 use Rector\ArgTyper\Tests\Rector\Rector\ClassMethod\AddClassMethodParamTypeRector\Fixture\KeepDateTimeInterface;
 use Rector\ArgTyper\Tests\Rector\Rector\ClassMethod\AddClassMethodParamTypeRector\Fixture\KeepNullableDateTimeInterface;
@@ -35,6 +36,7 @@ public function test(string $filePath): void
             new ClassMethodType(KeepNullableDateTimeInterface::class, 'record', 0, 'object:' . \DateTime::class),
             new ClassMethodType(KeepDateTimeInterface::class, 'record', 0, 'object:' . \DateTime::class),
             new ClassMethodType(SkipIntToFloatOverride::class, 'passInteger', 0, IntegerType::class),
+            new ClassMethodType(AddNullableForDefaultNull::class, 'run', 0, StringType::class),
             new ClassMethodType(KeepNullableScalarParam::class, 'translate', 0, StringType::class),
             new ClassMethodType(AddNullableScalarFromNullDefault::class, 'translate', 0, StringType::class),
         ];
diff --git a/tests/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector/Fixture/add_nullable_for_default_null.php.inc b/tests/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector/Fixture/add_nullable_for_default_null.php.inc
new file mode 100644
index 00000000..e6a45dec
--- /dev/null
+++ b/tests/Rector/Rector/ClassMethod/AddClassMethodParamTypeRector/Fixture/add_nullable_for_default_null.php.inc
@@ -0,0 +1,25 @@
+<?php
+
+namespace Rector\ArgTyper\Tests\Rector\Rector\ClassMethod\AddClassMethodParamTypeRector\Fixture;
+
+final class AddNullableForDefaultNull
+{
+    public function run($value = null)
+    {
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\ArgTyper\Tests\Rector\Rector\ClassMethod\AddClassMethodParamTypeRector\Fixture;
+
+final class AddNullableForDefaultNull
+{
+    public function run(?string $value = null)
+    {
+    }
+}
+
+?>
diff --git a/tests/Rector/Rector/Function_/AddFunctionParamTypeRector/AddFunctionParamTypeRectorTest.php b/tests/Rector/Rector/Function_/AddFunctionParamTypeRector/AddFunctionParamTypeRectorTest.php
index e53eb5ba..7d57af80 100644
--- a/tests/Rector/Rector/Function_/AddFunctionParamTypeRector/AddFunctionParamTypeRectorTest.php
+++ b/tests/Rector/Rector/Function_/AddFunctionParamTypeRector/AddFunctionParamTypeRectorTest.php
@@ -28,6 +28,11 @@ public function test(string $filePath): void
                 0,
                 StringType::class
             ),
+            new FuncCallType(
+                'Rector\ArgTyper\Tests\Rector\Rector\Function_\AddFunctionParamTypeRector\Fixture\defaultNullFunction',
+                0,
+                StringType::class
+            ),
         ]);
 
         $this->doTestFile($filePath);
diff --git a/tests/Rector/Rector/Function_/AddFunctionParamTypeRector/Fixture/default_null_function.php.inc b/tests/Rector/Rector/Function_/AddFunctionParamTypeRector/Fixture/default_null_function.php.inc
new file mode 100644
index 00000000..05f711cb
--- /dev/null
+++ b/tests/Rector/Rector/Function_/AddFunctionParamTypeRector/Fixture/default_null_function.php.inc
@@ -0,0 +1,19 @@
+<?php
+
+namespace Rector\ArgTyper\Tests\Rector\Rector\Function_\AddFunctionParamTypeRector\Fixture;
+
+function defaultNullFunction($item = null)
+{
+}
+
+?>
+-----
+<?php
+
+namespace Rector\ArgTyper\Tests\Rector\Rector\Function_\AddFunctionParamTypeRector\Fixture;
+
+function defaultNullFunction(?string $item = null)
+{
+}
+
+?>