diff -r 18863bf3501f -r e0b8b019d2f5 src/java.base/share/classes/java/time/YearMonth.java
--- a/src/java.base/share/classes/java/time/YearMonth.java	Thu Aug 29 18:52:30 2019 -0400
+++ b/src/java.base/share/classes/java/time/YearMonth.java	Thu Aug 29 16:31:34 2019 -0700
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2019, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -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");
     }