--- old/src/java.base/share/classes/java/time/Period.java	2019-08-27 17:28:31.414324386 -0700
+++ new/src/java.base/share/classes/java/time/Period.java	2019-08-27 17:28:31.226324386 -0700
@@ -140,6 +140,7 @@
     /**
      * Serialization version.
      */
+    @java.io.Serial
     private static final long serialVersionUID = -3587258372562876L;
     /**
      * The pattern for parsing.
@@ -1052,6 +1053,7 @@
      *
      * @return the instance of {@code Ser}, not null
      */
+    @java.io.Serial
     private Object writeReplace() {
         return new Ser(Ser.PERIOD_TYPE, this);
     }
@@ -1062,6 +1064,7 @@
      * @param s the stream to read
      * @throws java.io.InvalidObjectException always
      */
+    @java.io.Serial
     private void readObject(ObjectInputStream s) throws InvalidObjectException {
         throw new InvalidObjectException("Deserialization via serialization delegate");
     }