diff --git a/libraries/AP_HAL_ChibiOS/hwdef/iomcu/hwdef.dat b/libraries/AP_HAL_ChibiOS/hwdef/iomcu/hwdef.dat
index 5421973872..70bf534af5 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/iomcu/hwdef.dat
+++ b/libraries/AP_HAL_ChibiOS/hwdef/iomcu/hwdef.dat
@@ -98,5 +98,6 @@ define DMA_RESERVE_SIZE 0
 
 define IOMCU_FW TRUE
 
+IOMCU_FW 1
 MAIN_STACK 0x200
 PROCESS_STACK 0x250
\ No newline at end of file
diff --git a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
index 93a97c48ee..bb39a2a16c 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
+++ b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
@@ -487,7 +487,12 @@ def write_mcu_config(f):
         env_vars['MAIN_STACK'] = get_config('MAIN_STACK')
     else:
         env_vars['MAIN_STACK'] = "0x400"
-    
+
+    if get_config('IOMCU_FW', required=False):
+        env_vars['IOMCU_FW'] = get_config('IOMCU_FW')
+    else:
+        env_vars['IOMCU_FW'] = 0
+
     # write any custom STM32 defines
     for d in alllines:
         if d.startswith('STM32_'):