diff --git a/protocol/errors.json b/protocol/errors.json
index 3c432ec..32226b7 100644
--- a/protocol/errors.json
+++ b/protocol/errors.json
@@ -33,6 +33,7 @@
   "40032": "Invalid publish request (impermissible extras field)",
   "40033": "Operation cancelled",
   "40034": "Invalid publish request (maximum number of messages per ChannelMessage exceeded)",
+  "40035": "integration rule messageFilter regex must be RE2-compatible; backreferences and lookaround aren't supported",
   "40099": "Reserved for artifical errors for testing",
 
   "40100": "unauthorized",