diff --git a/src/node/handler/PadMessageHandler.js b/src/node/handler/PadMessageHandler.js
index 2cbe28755..00b1b5f98 100644
--- a/src/node/handler/PadMessageHandler.js
+++ b/src/node/handler/PadMessageHandler.js
@@ -446,7 +446,7 @@ exports.sendChatMessageToPadClients = async (mt, puId, text = null, padId = null
   // pad.appendChatMessage() ignores the displayName property so we don't need to wait for
   // authorManager.getAuthorName() to resolve before saving the message to the database.
   const promise = pad.appendChatMessage(message);
-  message.displayName = await authorManager.getAuthorName(message.userId);
+  message.displayName = await authorManager.getAuthorName(message.authorId);
   socketio.sockets.in(padId).json.send({
     type: 'COLLABROOM',
     data: {type: 'CHAT_MESSAGE', message},
diff --git a/src/static/js/ChatMessage.js b/src/static/js/ChatMessage.js
index b4658575e..98c5c4c0a 100644
--- a/src/static/js/ChatMessage.js
+++ b/src/static/js/ChatMessage.js
@@ -1,5 +1,7 @@
 'use strict';
 
+const {padutils: {warnDeprecated}} = require('./pad_utils');
+
 /**
  * Represents a chat message stored in the database and transmitted among users. Plugins can extend
  * the object with additional properties.
@@ -52,8 +54,14 @@ class ChatMessage {
    * @deprecated Use `authorId` instead.
    * @type {string}
    */
-  get userId() { return this.authorId; }
-  set userId(val) { this.authorId = val; }
+  get userId() {
+    warnDeprecated('ChatMessage.userId property is deprecated; use .authorId instead');
+    return this.authorId;
+  }
+  set userId(val) {
+    warnDeprecated('ChatMessage.userId property is deprecated; use .authorId instead');
+    this.authorId = val;
+  }
 
   /**
    * Alias of `displayName`, for compatibility with old plugins.
@@ -61,8 +69,14 @@ class ChatMessage {
    * @deprecated Use `displayName` instead.
    * @type {string}
    */
-  get userName() { return this.displayName; }
-  set userName(val) { this.displayName = val; }
+  get userName() {
+    warnDeprecated('ChatMessage.userName property is deprecated; use .displayName instead');
+    return this.displayName;
+  }
+  set userName(val) {
+    warnDeprecated('ChatMessage.userName property is deprecated; use .displayName instead');
+    this.displayName = val;
+  }
 
   // TODO: Delete this method once users are unlikely to roll back to a version of Etherpad that
   // doesn't support authorId and displayName.