diff --git a/stubs/runtime/ReflectionAttribute.php b/stubs/runtime/ReflectionAttribute.php
index 1634812f0..19fe0a66f 100644
--- a/stubs/runtime/ReflectionAttribute.php
+++ b/stubs/runtime/ReflectionAttribute.php
@@ -7,6 +7,9 @@
 
 	class ReflectionAttribute
 	{
+
+		public const IS_INSTANCEOF = 2;
+
 		public function getName(): string
 		{
 		}