diff --git a/core/Tron.proto b/core/Tron.proto
index 30a5c360846..b455bd3a146 100644
--- a/core/Tron.proto
+++ b/core/Tron.proto
@@ -261,6 +261,7 @@ enum ReasonCode {
   INCOMPATIBLE_VERSION = 0x18;
   INCOMPATIBLE_CHAIN = 0x19;
   TIME_OUT = 0x20;
+  CONNECT_FAIL = 0x21;
   UNKNOWN = 0xFF;
 }