diff --git a/Makefile b/Makefile
index a006551..518c1e8 100644
--- a/Makefile
+++ b/Makefile
@@ -53,6 +53,8 @@ startup_stm32f103xe.s
 # binaries
 #######################################
 PREFIX = ~/gcc-arm-none-eabi-7-2018-q2-update/bin/arm-none-eabi-
+#PREFIX = ~/gcc-arm-none-eabi-6-2017-q2-update/bin/arm-none-eabi-
+
 CC = $(PREFIX)gcc
 AS = $(PREFIX)gcc -x assembler-with-cpp
 CP = $(PREFIX)objcopy