diff --git a/rules-tests/DowngradePhp82/Rector/FunctionLike/DowngradeStandaloneNullTrueFalseReturnTypeRector/Fixture/in_arrow_function.php.inc b/rules-tests/DowngradePhp82/Rector/FunctionLike/DowngradeStandaloneNullTrueFalseReturnTypeRector/Fixture/in_arrow_function.php.inc
new file mode 100644
index 00000000..7c1f830b
--- /dev/null
+++ b/rules-tests/DowngradePhp82/Rector/FunctionLike/DowngradeStandaloneNullTrueFalseReturnTypeRector/Fixture/in_arrow_function.php.inc
@@ -0,0 +1,15 @@
+<?php
+
+namespace Rector\Tests\DowngradePhp82\Rector\Class_\DowngradeStandaloneNullTrueFalseReturnTypeRector\Fixture;
+
+fn (): null => null;
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\DowngradePhp82\Rector\Class_\DowngradeStandaloneNullTrueFalseReturnTypeRector\Fixture;
+
+fn (): mixed => null;
+
+?>
\ No newline at end of file
diff --git a/rules/DowngradePhp82/Rector/FunctionLike/DowngradeStandaloneNullTrueFalseReturnTypeRector.php b/rules/DowngradePhp82/Rector/FunctionLike/DowngradeStandaloneNullTrueFalseReturnTypeRector.php
index 2263f99e..f4d9afcd 100644
--- a/rules/DowngradePhp82/Rector/FunctionLike/DowngradeStandaloneNullTrueFalseReturnTypeRector.php
+++ b/rules/DowngradePhp82/Rector/FunctionLike/DowngradeStandaloneNullTrueFalseReturnTypeRector.php
@@ -9,8 +9,10 @@
 use PhpParser\Node\Expr\Closure;
 use PhpParser\Node\FunctionLike;
 use PhpParser\Node\Identifier;
+use PhpParser\Node\NullableType;
 use PhpParser\Node\Stmt\ClassMethod;
 use PhpParser\Node\Stmt\Function_;
+use PhpParser\Node\UnionType;
 use PHPStan\Type\Constant\ConstantBooleanType;
 use PHPStan\Type\NullType;
 use PHPStan\Type\Type;
@@ -118,7 +120,7 @@ private function resolveNativeType(Node $node, Node $returnType): Node
     {
         if ($node instanceof ClassMethod) {
             $returnTypeFromParent = $this->resolveParentNativeReturnType($node);
-            if ($returnTypeFromParent instanceof Node) {
+            if ($returnTypeFromParent instanceof UnionType || $returnTypeFromParent instanceof NullableType) {
                 $this->traverseNodesWithCallable($returnTypeFromParent, static function (Node $subNode): void {
                     $subNode->setAttribute(AttributeKey::ORIGINAL_NODE, null);
                 });