diff --git a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
index 8bc45c77e6..7703d6079a 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
+++ b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
@@ -2960,6 +2960,11 @@ def add_bootloader_defaults(f):
 #define HAL_GYROFFT_ENABLED 0
 #endif
 
+// bootloaders don't talk to the GCS:
+#ifndef HAL_GCS_ENABLED
+#define HAL_GCS_ENABLED 0
+#endif
+
 #define HAL_MAX_CAN_PROTOCOL_DRIVERS 0
 ''')