diff --git a/codec/src/main/java/io/netty/handler/codec/MessageToMessageCodec.java b/codec/src/main/java/io/netty/handler/codec/MessageToMessageCodec.java
index 8f22b7b2e7..ef559a7caa 100644
--- a/codec/src/main/java/io/netty/handler/codec/MessageToMessageCodec.java
+++ b/codec/src/main/java/io/netty/handler/codec/MessageToMessageCodec.java
@@ -15,6 +15,7 @@
  */
 package io.netty.handler.codec;
 
+import io.netty.buffer.ReferenceCounted;
 import io.netty.channel.ChannelDuplexHandler;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelPromise;
@@ -45,6 +46,10 @@ import io.netty.util.internal.TypeParameterMatcher;
  *         }
  *     }
  * </pre>
+ *
+ * Be aware that you need to call {@link ReferenceCounted#retain()} on messages that are just passed through if they
+ * are of type {@link ReferenceCounted}. This is needed as the {@link MessageToMessageCodec} will call
+ * {@link ReferenceCounted#release()} on encoded / decoded messages.
  */
 public abstract class MessageToMessageCodec<INBOUND_IN, OUTBOUND_IN> extends ChannelDuplexHandler {
 
diff --git a/codec/src/main/java/io/netty/handler/codec/MessageToMessageDecoder.java b/codec/src/main/java/io/netty/handler/codec/MessageToMessageDecoder.java
index e1851778fb..50d85c9c4d 100644
--- a/codec/src/main/java/io/netty/handler/codec/MessageToMessageDecoder.java
+++ b/codec/src/main/java/io/netty/handler/codec/MessageToMessageDecoder.java
@@ -16,13 +16,15 @@
 package io.netty.handler.codec;
 
 import io.netty.buffer.ByteBufUtil;
+import io.netty.buffer.ReferenceCounted;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.MessageList;
 import io.netty.util.internal.TypeParameterMatcher;
 
 /**
- * {@link ChannelInboundHandlerAdapter} which decodes from one message to an other message
+ * {@link ChannelInboundHandlerAdapter} which decodes from one message to an other message.
+ *
  *
  * For example here is an implementation which decodes a {@link String} to an {@link Integer} which represent
  * the length of the {@link String}.
@@ -39,6 +41,10 @@ import io.netty.util.internal.TypeParameterMatcher;
  *     }
  * </pre>
  *
+ * Be aware that you need to call {@link ReferenceCounted#retain()} on messages that are just passed through if they
+ * are of type {@link ReferenceCounted}. This is needed as the {@link MessageToMessageDecoder} will call
+ * {@link ReferenceCounted#release()} on decoded messages.
+ *
  */
 public abstract class MessageToMessageDecoder<I> extends ChannelInboundHandlerAdapter {
 
diff --git a/codec/src/main/java/io/netty/handler/codec/MessageToMessageEncoder.java b/codec/src/main/java/io/netty/handler/codec/MessageToMessageEncoder.java
index 8e119f5300..8d5bd6572a 100644
--- a/codec/src/main/java/io/netty/handler/codec/MessageToMessageEncoder.java
+++ b/codec/src/main/java/io/netty/handler/codec/MessageToMessageEncoder.java
@@ -16,6 +16,7 @@
 package io.netty.handler.codec;
 
 import io.netty.buffer.ByteBufUtil;
+import io.netty.buffer.ReferenceCounted;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelOutboundHandlerAdapter;
 import io.netty.channel.ChannelPromise;
@@ -39,6 +40,9 @@ import io.netty.util.internal.TypeParameterMatcher;
  *     }
  * </pre>
  *
+ * Be aware that you need to call {@link ReferenceCounted#retain()} on messages that are just passed through if they
+ * are of type {@link ReferenceCounted}. This is needed as the {@link MessageToMessageEncoder} will call
+ * {@link ReferenceCounted#release()} on encoded messages.
  */
 public abstract class MessageToMessageEncoder<I> extends ChannelOutboundHandlerAdapter {