--- old/src/java.base/share/classes/java/time/ZoneId.java	2019-08-27 17:28:33.526324386 -0700
+++ new/src/java.base/share/classes/java/time/ZoneId.java	2019-08-27 17:28:33.354324386 -0700
@@ -254,6 +254,7 @@
     /**
      * Serialization version.
      */
+    @java.io.Serial
     private static final long serialVersionUID = 8352817235686L;
 
     //-----------------------------------------------------------------------
@@ -624,6 +625,7 @@
      * @param s the stream to read
      * @throws InvalidObjectException always
      */
+    @java.io.Serial
     private void readObject(ObjectInputStream s) throws InvalidObjectException {
         throw new InvalidObjectException("Deserialization via serialization delegate");
     }
@@ -655,6 +657,7 @@
      * @return the instance of {@code Ser}, not null
      */
     // this is here for serialization Javadoc
+    @java.io.Serial
     private Object writeReplace() {
         return new Ser(Ser.ZONE_REGION_TYPE, this);
     }