diff --git a/libraries/AP_HAL_ChibiOS/Util.cpp b/libraries/AP_HAL_ChibiOS/Util.cpp
index 7f71ef4ebb..b13eda7605 100644
--- a/libraries/AP_HAL_ChibiOS/Util.cpp
+++ b/libraries/AP_HAL_ChibiOS/Util.cpp
@@ -252,12 +252,11 @@ bool Util::get_system_id(char buf[40])
     strncpy(board_name, CHIBIOS_SHORT_BOARD_NAME, 13);
     board_name[13] = 0;
     
-    // this format is chosen to match the human_readable_serial()
-    // function in auth.c
+    // this format is chosen to match the format used by HAL_PX4
     snprintf(buf, 40, "%s %02X%02X%02X%02X %02X%02X%02X%02X %02X%02X%02X%02X",
              board_name,
-             (unsigned)serialid[0], (unsigned)serialid[1], (unsigned)serialid[2], (unsigned)serialid[3], 
-             (unsigned)serialid[4], (unsigned)serialid[5], (unsigned)serialid[6], (unsigned)serialid[7], 
-             (unsigned)serialid[8], (unsigned)serialid[9], (unsigned)serialid[10],(unsigned)serialid[11]); 
+             (unsigned)serialid[3], (unsigned)serialid[2], (unsigned)serialid[1], (unsigned)serialid[0], 
+             (unsigned)serialid[7], (unsigned)serialid[6], (unsigned)serialid[5], (unsigned)serialid[4], 
+             (unsigned)serialid[11], (unsigned)serialid[10], (unsigned)serialid[9],(unsigned)serialid[8]); 
     return true;
 }