diff --git a/libraries/AP_InternalError/AP_InternalError.h b/libraries/AP_InternalError/AP_InternalError.h
index 56d9e86552..49a6e15154 100644
--- a/libraries/AP_InternalError/AP_InternalError.h
+++ b/libraries/AP_InternalError/AP_InternalError.h
@@ -52,6 +52,7 @@ public:
         gcs_bad_missionprotocol_link= (1U << 16),
         bitmask_range               = (1U << 17),
         gcs_offset                  = (1U << 18),
+        i2c_isr                     = (1U << 19),
     };
 
     void error(const AP_InternalError::error_t error);