--- Makefile
+++ Makefile
@@ -1,9 +1,9 @@
 ALL=snooze
 
-CFLAGS=-g -O2 -Wall -Wextra -Wwrite-strings
+CFLAGS+=-g -Wall -Wextra -Wwrite-strings
 
 DESTDIR=
-PREFIX=/usr/local
+PREFIX?=/usr/local
 BINDIR=$(PREFIX)/bin
 MANDIR=$(PREFIX)/share/man