diff --git a/heart_rate_sensor_protocol.h b/heart_rate_sensor_protocol.h
index 9128e05..90386e2 100644
--- a/heart_rate_sensor_protocol.h
+++ b/heart_rate_sensor_protocol.h
@@ -27,6 +27,7 @@ typedef enum {
 
   kifyhrs_ecode_overtime         = 200,
   kifyhrs_ecode_channel_is_close = 201,
+  kifyhrs_ecode_upper_exception  = 202,
 
 } ify_hrs_error_code_t;
 
@@ -60,6 +61,9 @@ static inline const char *ify_hrs_error_code_to_string(ify_hrs_error_code_t code
       return "overtime";
     case kifyhrs_ecode_channel_is_close:
       return "channel is close";
+
+    case kifyhrs_ecode_upper_exception:
+      return "upper exception";
     default:
       return "unkown error";
   }