diff --git a/protocol_parser.cpp b/protocol_parser.cpp
index ef25e55..2a87956 100644
--- a/protocol_parser.cpp
+++ b/protocol_parser.cpp
@@ -23,7 +23,7 @@ using namespace std;
   }
 
 #define PROCESS_PACKET_XX_END(ackNum)        \
-  if (ecode != 0) {                          \
+  if (ecode == 0) {                          \
     m_cancmder->sendAck(rxcmd, ack, ackNum); \
     return;                                  \
   }                                          \