diff --git a/Marlin/SanityCheck.h b/Marlin/SanityCheck.h
index 10f0eec20..8f7ca2ecb 100644
--- a/Marlin/SanityCheck.h
+++ b/Marlin/SanityCheck.h
@@ -283,6 +283,10 @@
   #error "SERIAL_XON_XOFF and SERIAL_STATS_* features not supported on USB-native AVR devices."
 #endif
 
+#if SERIAL_PORT > 7
+  #error "Set SERIAL_PORT to the port on your board. Usually this is 0."
+#endif
+
 /**
  * Dual Stepper Drivers
  */