diff --git a/rules/DeadCode/Rector/If_/RemoveDeadInstanceOfRector.php b/rules/DeadCode/Rector/If_/RemoveDeadInstanceOfRector.php
index b41d0b18bd5..4003d586319 100644
--- a/rules/DeadCode/Rector/If_/RemoveDeadInstanceOfRector.php
+++ b/rules/DeadCode/Rector/If_/RemoveDeadInstanceOfRector.php
@@ -14,12 +14,14 @@
 use PhpParser\Node\Expr\PropertyFetch;
 use PhpParser\Node\Expr\StaticPropertyFetch;
 use PhpParser\Node\Name;
+use PhpParser\Node\Name\FullyQualified;
 use PhpParser\Node\Stmt;
 use PhpParser\Node\Stmt\Expression;
 use PhpParser\Node\Stmt\If_;
 use PhpParser\NodeTraverser;
 use PHPStan\Reflection\ClassReflection;
 use PHPStan\Type\MixedType;
+use PHPStan\Type\ObjectType;
 use Rector\NodeManipulator\IfManipulator;
 use Rector\Rector\AbstractRector;
 use Rector\Reflection\ReflectionResolver;
@@ -156,14 +158,17 @@ private function isInstanceofTheSameType(Instanceof_ $instanceof): ?bool
             return null;
         }
 
-        $classType = $this->nodeTypeResolver->getType($instanceof->class);
-        $exprType = $this->nodeTypeResolver->getNativeType($instanceof->expr);
+        if (! $instanceof->class instanceof FullyQualified) {
+            return null;
+        }
 
-        if ($classType->equals($exprType)) {
-            return true;
+        $exprType = $this->nodeTypeResolver->getNativeType($instanceof->expr);
+        if (! $exprType instanceof ObjectType) {
+            return null;
         }
 
-        return $classType->isSuperTypeOf($exprType)
+        $className = $instanceof->class->toString();
+        return $exprType->isInstanceOf($className)
             ->yes();
     }
 
diff --git a/tests/Issues/Issue6480/Fixture/fixture.php.inc b/tests/Issues/Issue6480/Fixture/fixture.php.inc
index 1720dc7905d..2cdf0985bdf 100644
--- a/tests/Issues/Issue6480/Fixture/fixture.php.inc
+++ b/tests/Issues/Issue6480/Fixture/fixture.php.inc
@@ -2,10 +2,12 @@
 
 namespace Rector\Tests\Issues\Issue6480\Fixture;
 
+use Rector\Tests\Issues\Issue6480\Source\ExistingClass;
+
 class Fixture
 {
-    function test(Foo $foo, mixed $bar): void {
-        if ($foo instanceof Foo) {
+    function test(ExistingClass $foo, mixed $bar): void {
+        if ($foo instanceof ExistingClass) {
             var_dump(!empty($bar) ? $bar : null);
         }
     }
@@ -17,9 +19,11 @@ class Fixture
 
 namespace Rector\Tests\Issues\Issue6480\Fixture;
 
+use Rector\Tests\Issues\Issue6480\Source\ExistingClass;
+
 class Fixture
 {
-    function test(Foo $foo, mixed $bar): void {
+    function test(ExistingClass $foo, mixed $bar): void {
         var_dump(empty($bar) ? null : $bar);
     }
 }
diff --git a/tests/Issues/Issue6480/Source/ExistingClass.php b/tests/Issues/Issue6480/Source/ExistingClass.php
new file mode 100644
index 00000000000..1b1cea4afcd
--- /dev/null
+++ b/tests/Issues/Issue6480/Source/ExistingClass.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\Tests\Issues\Issue6480\Source;
+
+final class ExistingClass
+{
+
+}