--- old/src/java.base/share/classes/java/time/ZoneOffset.java	2019-08-27 17:28:34.114324386 -0700
+++ new/src/java.base/share/classes/java/time/ZoneOffset.java	2019-08-27 17:28:33.850324386 -0700
@@ -143,6 +143,7 @@
     /**
      * Serialization version.
      */
+    @java.io.Serial
     private static final long serialVersionUID = 2357656521762053153L;
 
     /**
@@ -763,6 +764,7 @@
      *
      * @return the instance of {@code Ser}, not null
      */
+    @java.io.Serial
     private Object writeReplace() {
         return new Ser(Ser.ZONE_OFFSET_TYPE, this);
     }
@@ -773,6 +775,7 @@
      * @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");
     }