--- a/Makefile.in
+++ b/Makefile.in
@@ -1,7 +1,7 @@
-CC = gcc
-CFLAGS =
-EXTRA_CFLAGS = -Wall -Wextra
-DESTDIR =
+CC ?= gcc
+CFLAGS ?=
+EXTRA_CFLAGS ?= -Wall -Wextra
+DESTDIR ?=
 
 ENABLE_SYSTEMD =
 ENABLE_ELOGIND =
