diff --git a/src/JsonSchema/Constraints/UndefinedConstraint.php b/src/JsonSchema/Constraints/UndefinedConstraint.php
index cc41058a..d0482007 100644
--- a/src/JsonSchema/Constraints/UndefinedConstraint.php
+++ b/src/JsonSchema/Constraints/UndefinedConstraint.php
@@ -21,6 +21,7 @@
  * @author Robert Schönthal <seroscho@googlemail.com>
  * @author Bruno Prieto Reis <bruno.p.reis@gmail.com>
  */
+#[\AllowDynamicProperties]
 class UndefinedConstraint extends Constraint
 {
     /**