diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index e89503f7..dbc6ad60 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -104,3 +104,8 @@ parameters:
 			message: "#^Call to an undefined method PHPStan\\\\Type\\\\Type\\:\\:getValue\\(\\)\\.$#"
 			count: 1
 			path: src/Drupal9/Rector/Deprecation/ExtensionPathRector.php
+
+		-
+			message: "#^Doing instanceof PHPStan\\\\Type\\\\ObjectType is error\\-prone and deprecated\\. Use Type\\:\\:isObject\\(\\) or Type\\:\\:getObjectClassNames\\(\\) instead\\.$#"
+			count: 1
+			path: src/Rector/Class_/FunctionalTestDefaultThemePropertyRector.php
diff --git a/src/Rector/Class_/FunctionalTestDefaultThemePropertyRector.php b/src/Rector/Class_/FunctionalTestDefaultThemePropertyRector.php
index 7fe3eeeb..aeba2ead 100644
--- a/src/Rector/Class_/FunctionalTestDefaultThemePropertyRector.php
+++ b/src/Rector/Class_/FunctionalTestDefaultThemePropertyRector.php
@@ -8,6 +8,7 @@
 use PhpParser\Builder\Property;
 use PhpParser\Node;
 use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\Php\PhpPropertyReflection;
 use PHPStan\Type\ObjectType;
 use Rector\BetterPhpDocParser\PhpDocInfo\PhpDocInfoFactory;
 use Rector\Core\Exception\ShouldNotHappenException;
@@ -24,19 +25,19 @@
 final class FunctionalTestDefaultThemePropertyRector extends AbstractScopeAwareRector
 {
     /**
-     * @var \Rector\Core\PhpParser\Node\Value\ValueResolver
+     * @var \Rector\BetterPhpDocParser\PhpDocInfo\PhpDocInfoFactory
      */
-    private ValueResolver $valueResolver;
+    private PhpDocInfoFactory $phpDocInfoFactory;
 
     /**
-     * @var \Rector\BetterPhpDocParser\PhpDocInfo\PhpDocInfoFactory
+     * @var \Rector\Core\PhpParser\Node\Value\ValueResolver
      */
-    private PhpDocInfoFactory $phpDocInfoFactory;
+    private ValueResolver $valueResolver;
 
     public function __construct(ValueResolver $valueResolver, PhpDocInfoFactory $phpDocInfoFactory)
     {
-        $this->valueResolver = $valueResolver;
         $this->phpDocInfoFactory = $phpDocInfoFactory;
+        $this->valueResolver = $valueResolver;
     }
 
     public function getRuleDefinition(): RuleDefinition
@@ -76,9 +77,12 @@ public function refactorWithScope(Node $node, Scope $scope): ?Node
             return null;
         }
         $type = $this->nodeTypeResolver->getType($node);
-        if (!$type instanceof ObjectType) {
-            throw new ShouldNotHappenException(__CLASS__.' type for node was not '.ObjectType::class);
+
+        if(count($type->getObjectClassNames()) === 0 || !$type->isObject()->yes()) {
+            return null;
         }
+
+        assert($type instanceof ObjectType);
         $browserTestBaseType = new ObjectType(BrowserTestBase::class);
         if ($type->isSmallerThanOrEqual($browserTestBaseType)->yes()) {
             return null;
@@ -92,10 +96,13 @@ public function refactorWithScope(Node $node, Scope $scope): ?Node
         }
 
         $defaultThemeProperty = $classReflection->getProperty('defaultTheme', $scope);
+        assert($defaultThemeProperty instanceof \PHPStan\Reflection\Php\PhpPropertyReflection);
+
         $reflectionProperty = $defaultThemeProperty->getNativeReflection();
         $betterReflection = $reflectionProperty->getBetterReflection();
         $defaultValueExpression = $betterReflection->getDefaultValueExpression();
 
+
         if ($defaultValueExpression instanceof Node\Scalar\String_ && strlen($this->valueResolver->getValue($defaultValueExpression)) > 0) {
             return null;
         }