--- old/src/java.base/share/classes/java/time/YearMonth.java	2019-08-27 17:28:33.050324386 -0700
+++ new/src/java.base/share/classes/java/time/YearMonth.java	2019-08-27 17:28:32.870324386 -0700
@@ -134,6 +134,7 @@
     /**
      * Serialization version.
      */
+    @java.io.Serial
     private static final long serialVersionUID = 4183400860270640070L;
     /**
      * Parser.
@@ -1222,6 +1223,7 @@
      *
      * @return the instance of {@code Ser}, not null
      */
+    @java.io.Serial
     private Object writeReplace() {
         return new Ser(Ser.YEAR_MONTH_TYPE, this);
     }
@@ -1232,6 +1234,7 @@
      * @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");
     }