diff --git a/src/core/errors.ts b/src/core/errors.ts
index 241e441c..aa433426 100644
--- a/src/core/errors.ts
+++ b/src/core/errors.ts
@@ -4,6 +4,14 @@ import * as Ably from 'ably';
  * Error codes for the Chat SDK.
  */
 export enum ErrorCodes {
+  /**
+   * The message was rejected before publishing by a rule on the chat room.
+   *
+   * For example, a message may be rejected because it violates a moderation policy
+   * that bans profanity.
+   */
+  MessageRejectedByBeforePublishRule = 42201,
+
   /**
    * The messages feature failed to attach.
    */