diff --git a/include/sta/rtos/system/can_bus.hpp b/include/sta/rtos/system/can_bus.hpp
index 906af71..86471fe 100644
--- a/include/sta/rtos/system/can_bus.hpp
+++ b/include/sta/rtos/system/can_bus.hpp
@@ -76,6 +76,10 @@
  * @brief CAN system message in queue.
  */
 #define STA_RTOS_CAN_FLAG_SYS_QUEUED    0x1U << 3
+/**
+ * @brief CAN mailbox complete.
+ */
+#define STA_RTOS_TX_MAILBOX_COMPLETE 	0x1U << 4
 
 /**
  * @brief CAN SID bits used for system messages.