--- old/src/java.base/share/classes/java/time/chrono/ChronoPeriodImpl.java	2019-08-27 17:28:37.530324386 -0700
+++ new/src/java.base/share/classes/java/time/chrono/ChronoPeriodImpl.java	2019-08-27 17:28:37.310324386 -0700
@@ -98,6 +98,7 @@
     /**
      * Serialization version.
      */
+    @java.io.Serial
     private static final long serialVersionUID = 57387258289L;
 
     /**
@@ -366,6 +367,7 @@
      *
      * @return the instance of {@code Ser}, not null
      */
+    @java.io.Serial
     protected Object writeReplace() {
         return new Ser(Ser.CHRONO_PERIOD_TYPE, this);
     }
@@ -376,6 +378,7 @@
      * @param s the stream to read
      * @throws InvalidObjectException always
      */
+    @java.io.Serial
     private void readObject(ObjectInputStream s) throws ObjectStreamException {
         throw new InvalidObjectException("Deserialization via serialization delegate");
     }