diff --git a/spring-jms/src/main/java/org/springframework/jms/core/MessagePostProcessor.java b/spring-jms/src/main/java/org/springframework/jms/core/MessagePostProcessor.java
index c36c7dafb66..84c4c5da944 100644
--- a/spring-jms/src/main/java/org/springframework/jms/core/MessagePostProcessor.java
+++ b/spring-jms/src/main/java/org/springframework/jms/core/MessagePostProcessor.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2005 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,11 +20,12 @@ import javax.jms.JMSException;
 import javax.jms.Message;
 
 /**
- * To be used with JmsTemplate's send method that convert an object to a message.
- * It allows for further modification of the message after it has been processed
- * by the converter. This is useful for setting of JMS Header and Properties.
+ * To be used with JmsTemplate's send method that converts an object to a message.
  *
- * <p>This often as an anonymous class within a method implementation.
+ * <p>This allows for further modification of the message after it has been processed
+ * by the converter and is useful for setting JMS headers and properties.
+ *
+ * <p>Often implemented as a lambda expression or as an anonymous inner class.
  *
  * @author Mark Pollack
  * @since 1.1
@@ -32,13 +33,15 @@ import javax.jms.Message;
  * @see JmsTemplate#convertAndSend(javax.jms.Destination, Object, MessagePostProcessor)
  * @see org.springframework.jms.support.converter.MessageConverter
  */
+@FunctionalInterface
 public interface MessagePostProcessor {
 
 	/**
-	 * Apply a MessagePostProcessor to the message. The returned message is
-	 * typically a modified version of the original.
+	 * Process the given message.
+	 * <p>The returned message is typically a modified version of the original.
 	 * @param message the JMS message from the MessageConverter
-	 * @return the modified version of the Message
+	 * @return a post-processed variant of the message, or simply the incoming
+	 * message; never {@code null}
 	 * @throws javax.jms.JMSException if thrown by JMS API methods
 	 */
 	Message postProcessMessage(Message message) throws JMSException;
diff --git a/spring-messaging/src/main/java/org/springframework/messaging/core/MessagePostProcessor.java b/spring-messaging/src/main/java/org/springframework/messaging/core/MessagePostProcessor.java
index 92e78ef50e7..04e3dfcaea9 100644
--- a/spring-messaging/src/main/java/org/springframework/messaging/core/MessagePostProcessor.java
+++ b/spring-messaging/src/main/java/org/springframework/messaging/core/MessagePostProcessor.java
@@ -28,13 +28,14 @@ import org.springframework.messaging.Message;
  * @see MessageSendingOperations
  * @see MessageRequestReplyOperations
  */
+@FunctionalInterface
 public interface MessagePostProcessor {
 
 	/**
 	 * Process the given message.
 	 * @param message the message to process
-	 * @return a post-processed variant of the message,
-	 * or simply the incoming message; never {@code null}
+	 * @return a post-processed variant of the message, or simply the incoming
+	 * message; never {@code null}
 	 */
 	Message<?> postProcessMessage(Message<?> message);