diff --git a/core/Tron.proto b/core/Tron.proto
index d9800a4f710..87a0b6ca70b 100644
--- a/core/Tron.proto
+++ b/core/Tron.proto
@@ -201,6 +201,7 @@ enum ReasonCode {
   PING_TIMEOUT = 0x0B;
   USER_REASON = 0x10;
   RESET = 0x11;
+  SYNC_FAIL = 0x12;
   UNKNOWN = 0xFF;
 }