src/java.base/share/classes/java/lang/UnknownError.java

@@ -32,10 +32,11 @@
  * @author unascribed
  * @since   1.0
  */
 public
 class UnknownError extends VirtualMachineError {
+    @java.io.Serial
     private static final long serialVersionUID = 2524784860676771849L;
 
     /**
      * Constructs an <code>UnknownError</code> with no detail message.
      */