src/java.base/share/classes/java/time/chrono/ChronoPeriodImpl.java

*** 96,105 ****
--- 96,106 ----
      // this class is only used by JDK chronology implementations and makes assumptions based on that fact
  
      /**
       * Serialization version.
       */
+     @java.io.Serial
      private static final long serialVersionUID = 57387258289L;
  
      /**
       * The set of supported units.
       */
*** 364,383 ****
--- 365,386 ----
       *  out.writeInt(days);
       * </pre>
       *
       * @return the instance of {@code Ser}, not null
       */
+     @java.io.Serial
      protected Object writeReplace() {
          return new Ser(Ser.CHRONO_PERIOD_TYPE, this);
      }
  
      /**
       * Defend against malicious streams.
       *
       * @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");
      }
  
      void writeExternal(DataOutput out) throws IOException {