diff --git a/megaavr/cores/coreX-corefiles/Arduino.h b/megaavr/cores/coreX-corefiles/Arduino.h
index 664aab8..80b4557 100644
--- a/megaavr/cores/coreX-corefiles/Arduino.h
+++ b/megaavr/cores/coreX-corefiles/Arduino.h
@@ -28,6 +28,7 @@
 
 #undef F
 #define F(str) (str)
+#define __FlashStringHelper char
 
 #ifdef __cplusplus
 extern "C"{
@@ -71,7 +72,7 @@ extern "C"{
   #define _NOP() do { __asm__ volatile ("nop"); } while (0)
 #endif
 
-/* Allows performing a correction on the CPU value using the signature row 
+/* Allows performing a correction on the CPU value using the signature row
   values indicating oscillator error provided from the device manufacturer */
 #define PERFORM_SIGROW_CORRECTION_F_CPU 0