diff --git a/Marlin/src/core/serial.h b/Marlin/src/core/serial.h
index c2745e972b..bdf3ba4686 100644
--- a/Marlin/src/core/serial.h
+++ b/Marlin/src/core/serial.h
@@ -75,7 +75,7 @@ extern uint8_t marlin_debug_flags;
 #define SERIAL_PRINTF(V...)     SERIAL_OUT(printf, V)
 #define SERIAL_FLUSH()          SERIAL_OUT(flush)
 
-#ifdef __STM32F1__
+#ifdef ARDUINO_ARCH_STM32
   #define SERIAL_FLUSHTX()      SERIAL_OUT(flush)
 #elif TX_BUFFER_SIZE > 0
   #define SERIAL_FLUSHTX()      SERIAL_OUT(flushTX)