diff --git a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
index 88602c0d10..e6aedc3def 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
+++ b/libraries/AP_HAL_ChibiOS/hwdef/scripts/chibios_hwdef.py
@@ -1199,12 +1199,11 @@ def write_UART_config(f):
     devnames = "ABCDEFGHI"
     sdev = 0
     idx = 0
-    num_empty_uarts = 0
     for dev in uart_list:
         if dev == 'EMPTY':
             f.write('#define HAL_UART%s_DRIVER Empty::UARTDriver uart%sDriver\n' %
                     (devnames[idx], devnames[idx]))
-            num_empty_uarts += 1
+            sdev += 1
         else:
             f.write(
                 '#define HAL_UART%s_DRIVER ChibiOS::UARTDriver uart%sDriver(%u)\n'
@@ -1242,6 +1241,7 @@ def write_UART_config(f):
         elif dev.startswith('OTG'):
             n = int(dev[3:])
         elif dev.startswith('EMPTY'):
+            devlist.append('{}')
             continue
         else:
             error("Invalid element %s in UART_ORDER" % dev)
@@ -1307,7 +1307,7 @@ def write_UART_config(f):
         num_uarts -= 1
     if num_uarts > 9:
         error("Exceeded max num UARTs of 9 (%u)" % num_uarts)
-    f.write('#define HAL_UART_NUM_SERIAL_PORTS %u\n' % (num_uarts+num_empty_uarts))
+    f.write('#define HAL_UART_NUM_SERIAL_PORTS %u\n' % num_uarts)
 
 
 def write_UART_config_bootloader(f):