diff --git a/protocol/errors.json b/protocol/errors.json
index e9a09a5..8a943ed 100644
--- a/protocol/errors.json
+++ b/protocol/errors.json
@@ -30,6 +30,7 @@
   "40030": "Invalid publish request (unspecified)",
   "40031": "Invalid publish request (invalid client-specified id)",
   "40032": "Invalid publish request (impermissible extras field)",
+  "40033": "operation cancelled",
   "40099": "Reserved for artifical errors for testing",
 
   "40100": "unauthorized",