diff --git a/testing/makefiles/libcommon.mk b/testing/makefiles/libcommon.mk
index cd6ff52e..82c88ff0 100644
--- a/testing/makefiles/libcommon.mk
+++ b/testing/makefiles/libcommon.mk
@@ -1,4 +1,4 @@
-top_dir		:= $(dir $(lastword ${MAKEFILE_LIST}))../..
+top_dir		:= $(abspath $(dir $(lastword ${MAKEFILE_LIST}))../..)
 build_dir := ${top_dir}/_build
 
 include $(top_dir)/etc/makefiles/arduino-cli.mk