diff --git a/src/JsonSchema/Constraints/UndefinedConstraint.php b/src/JsonSchema/Constraints/UndefinedConstraint.php
index 8effd4ba..1e984a3d 100644
--- a/src/JsonSchema/Constraints/UndefinedConstraint.php
+++ b/src/JsonSchema/Constraints/UndefinedConstraint.php
@@ -20,6 +20,7 @@
  * @author Robert Schönthal <seroscho@googlemail.com>
  * @author Bruno Prieto Reis <bruno.p.reis@gmail.com>
  */
+#[\AllowDynamicProperties]
 class UndefinedConstraint extends Constraint
 {
     /**