diff --git a/Make.defaults b/Make.defaults
index 0585915..ccada22 100644
--- a/Make.defaults
+++ b/Make.defaults
@@ -38,14 +38,14 @@
 # Where to install the package. GNU-EFI will create and access
 # lib and include under the root
 #
-INSTALLROOT := /
-PREFIX := /usr/local
-LIBDIR := ${PREFIX}/lib
+INSTALLROOT ?= /
+PREFIX ?= /usr/local
+LIBDIR ?= ${PREFIX}/lib
 
 TOPDIR    := $(shell if [ "$$PWD" != "" ]; then echo $$PWD; else pwd; fi)
 
 HOSTARCH   = $(shell uname -m | sed s,i[3456789]86,ia32,)
-ARCH	   := $(shell uname -m | sed s,i[3456789]86,ia32,)
+ARCH	   ?= $(shell uname -m | sed s,i[3456789]86,ia32,)
 # FreeBSD (and possibly others) reports amd64 instead of x86_64
 ifeq ($(ARCH), amd64)
 ARCH	   = x86_64