diff --git a/Marlin/fastio.h b/Marlin/fastio.h
index 4b6ec4e495..bd6efe670e 100644
--- a/Marlin/fastio.h
+++ b/Marlin/fastio.h
@@ -38,7 +38,7 @@ typedef int8_t pin_t;
 #define AVR_ATmega1284_FAMILY (defined(__AVR_ATmega644__) || defined(__AVR_ATmega644P__) || defined(__AVR_ATmega644PA__) || defined(__AVR_ATmega1284P__))
 #define AVR_ATmega2560_FAMILY (defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__))
 #define AVR_ATmega2561_FAMILY (defined(__AVR_ATmega1281__) || defined(__AVR_ATmega2561__))
-#define AVR_ATmega328_FAMILY (defined(__AVR_ATmega168__) || defined(__AVR_ATmega328__) || defined(__AVR_ATmega328p__))
+#define AVR_ATmega328_FAMILY (defined(__AVR_ATmega168__) || defined(__AVR_ATmega328__) || defined(__AVR_ATmega328P__))
 
 /**
  * Include Ports and Functions