diff --git a/rules/AnnotationsToAttributes/Rector/Class_/AnnotationWithValueToAttributeRector.php b/rules/AnnotationsToAttributes/Rector/Class_/AnnotationWithValueToAttributeRector.php
index 422dd761..03e05f02 100644
--- a/rules/AnnotationsToAttributes/Rector/Class_/AnnotationWithValueToAttributeRector.php
+++ b/rules/AnnotationsToAttributes/Rector/Class_/AnnotationWithValueToAttributeRector.php
@@ -134,7 +134,7 @@ public function refactor(Node $node): ?Node
                 );
 
                 if ($node instanceof ClassMethod && $annotationWithValueToAttribute->getIsOnClassLevel() && $this->currentClass instanceof Class_) {
-                    Assert::isInstanceOf($this->currentClass, Class_::class);
+                    Assert::isAOf($this->currentClass, Class_::class);
                     $this->currentClass->attrGroups = array_merge($this->currentClass->attrGroups, [$attributeGroup]);
                 } else {
                     $node->attrGroups = array_merge($node->attrGroups, [$attributeGroup]);