diff --git a/Sam.mk b/Sam.mk
index 2ec94ee..b18a6e6 100644
--- a/Sam.mk
+++ b/Sam.mk
@@ -114,7 +114,7 @@ endif
 ifndef ARDUINO_CORE_PATH
     ARDUINO_CORE_PATH   = $(ALTERNATE_CORE_PATH)/cores/arduino
 endif
-ifndef BOARD_TXT
+ifndef BOARDS_TXT
     BOARDS_TXT          = $(ALTERNATE_CORE_PATH)/boards.txt
 endif