--- old/src/java.base/share/classes/java/time/Duration.java	2019-08-27 17:28:26.958324386 -0700
+++ new/src/java.base/share/classes/java/time/Duration.java	2019-08-27 17:28:26.786324386 -0700
@@ -140,6 +140,7 @@
     /**
      * Serialization version.
      */
+    @java.io.Serial
     private static final long serialVersionUID = 3078945930695997490L;
     /**
      * Constant for nanos per second.
@@ -1529,6 +1530,7 @@
      *
      * @return the instance of {@code Ser}, not null
      */
+    @java.io.Serial
     private Object writeReplace() {
         return new Ser(Ser.DURATION_TYPE, this);
     }
@@ -1539,6 +1541,7 @@
      * @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");
     }