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

*** 32,41 ****
--- 32,42 ----
   * @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.
       */