diff --git a/Makefile b/Makefile
index 57be1b9..77bbd42 100644
--- a/Makefile
+++ b/Makefile
@@ -22,8 +22,8 @@
 
 
 ifeq ($(BOARD_HARDWARE_PATH),)
-PLUGIN_TEST_SUPPORT_DIR =? ./build-tools
-KALEIDOSCOPE_BUILDER_DIR =? ./avr/libraries/Kaleidoscope/bin/
+PLUGIN_TEST_SUPPORT_DIR ?= ./build-tools
+KALEIDOSCOPE_BUILDER_DIR ?= ./avr/libraries/Kaleidoscope/bin/
 
 endif