src/java.base/share/classes/java/util/IllformedLocaleException.java

@@ -39,10 +39,11 @@
  * @see Locale
  * @since 1.7
  */
 public class IllformedLocaleException extends RuntimeException {
 
+    @java.io.Serial
     private static final long serialVersionUID = -5245986824925681401L;
 
     private int _errIdx = -1;
 
     /**