--- a/makefile
+++ b/makefile
@@ -4,10 +4,10 @@
 # Installation directories:
 
 # Destination directory for installation (intended for packagers)
-DESTDIR =
+DESTDIR ?=
 
 # Root directory for final installation
-PREFIX = /usr
+PREFIX ?= /usr
 
 # Data file directory
 data_dir = ${PREFIX}/share/
