diff --git a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
index 1be49e5647..6a06440fe9 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
+++ b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
@@ -957,13 +957,18 @@ def write_mcu_config(f):
         f.write('#define CRT1_RAMFUNC_ENABLE FALSE\n')
 
     storage_flash_page = get_storage_flash_page()
+    flash_reserve_end = get_config('FLASH_RESERVE_END_KB', default=0, type=int)
     if storage_flash_page is not None:
         if not args.bootloader:
             f.write('#define STORAGE_FLASH_PAGE %u\n' % storage_flash_page)
             validate_flash_storage_size()
-        else:
+        elif get_config('FLASH_RESERVE_END_KB', type=int, required = False) is None:
             # ensure the flash page leaves room for bootloader
             offset = get_flash_page_offset_kb(storage_flash_page)
+            bl_offset = get_config('FLASH_BOOTLOADER_LOAD_KB', type=int)
+            # storage at end of flash - leave room
+            if offset > bl_offset:
+                flash_reserve_end = flash_size - offset
 
     if flash_size >= 2048 and not args.bootloader:
         # lets pick a flash sector for Crash log
@@ -980,7 +985,7 @@ def write_mcu_config(f):
                 'EXT_FLASH_RESERVE_START_KB', default=0, type=int)*1024))
             f.write('#define BOOT_FROM_EXT_FLASH 1\n')
         f.write('#define FLASH_BOOTLOADER_LOAD_KB %u\n' % get_config('FLASH_BOOTLOADER_LOAD_KB', type=int))
-        f.write('#define FLASH_RESERVE_END_KB %u\n' % get_config('FLASH_RESERVE_END_KB', default=0, type=int))
+        f.write('#define FLASH_RESERVE_END_KB %u\n' % flash_reserve_end)
         f.write('#define APP_START_OFFSET_KB %u\n' % get_config('APP_START_OFFSET_KB', default=0, type=int))
     f.write('\n')