diff --git a/Makefile b/Makefile
index 7d25a69fdf0aa5b001bdc7a3705eee12f90591e9..1961c4787c4d0b555e65a56d82f5202316216835 100644
--- a/Makefile
+++ b/Makefile
@@ -4,9 +4,8 @@ CONFIG_FILE=$(CURDIR)/config/Makefile.conf
 include $(CONFIG_FILE_DEFAULTS)
 include $(CONFIG_FILE)
 
-#list of offically supported config options; they should have a default value in CONFIG_FILE_DEFAULTS
-CONFIGURABLE=PRIMARY_ARCH SECONDARY_ARCH WORKSPACE ISO_BASE_URL ISO_RELEASE ISO_VERSION ISO_FLAVOR \
-	IMAGE_GIT_URL IMAGE_GIT_BRANCH
+#read all offically config options from CONFIG_FILE_DEFAULTS
+CONFIGURABLE=$(shell cat "$(CONFIG_FILE_DEFAULTS)" | grep -v "^\#" | cut -s -d"=" -f1)
 
 ifndef ARCH
   ARCH=$(PRIMARY_ARCH)