diff --git a/arduino-mk/Arduino.mk b/arduino-mk/Arduino.mk
index b217592..aaec9aa 100644
--- a/arduino-mk/Arduino.mk
+++ b/arduino-mk/Arduino.mk
@@ -306,10 +306,12 @@ ifndef AVR_TOOLS_DIR
     BUNDLED_AVR_TOOLS_DIR := $(call dir_if_exists,$(ARDUINO_DIR)/hardware/tools/avr)
     ifdef BUNDLED_AVR_TOOLS_DIR
         AVR_TOOLS_DIR     = $(BUNDLED_AVR_TOOLS_DIR)
-        # The avrdude bundled with Arduino can't find it's config
-        AVRDUDE_CONF	  = $(AVR_TOOLS_DIR)/etc/avrdude.conf
-        $(call show_config_variable,AVR_TOOLS_DIR,[BUNDLED],(in Arduino distribution))
-
+        # if AVRDUDE_CONF is already defined, don't overwrite it
+        ifndef AVRDUDE_CONF
+            # The avrdude bundled with Arduino can't find it's config
+            AVRDUDE_CONF	  = $(AVR_TOOLS_DIR)/etc/avrdude.conf
+            $(call show_config_variable,AVR_TOOLS_DIR,[BUNDLED],(in Arduino distribution))
+       endif
     else
 
         SYSTEMPATH_AVR_TOOLS_DIR := $(call dir_if_exists,$(abspath $(dir $(shell which avr-gcc))/..))