diff --git a/README b/README
index 8244b04b..2740f542 100644
--- a/README
+++ b/README
@@ -12,6 +12,7 @@ LIBNAME=lib64
 DESTDIR=/tmp/openrc-image
 MKNET=oldnet
 MKPAM=pam
+MKPREFIX=yes
 MKPKGCONFIG=no
 MKSELINUX=yes
 MKSTATICLIBS=no
@@ -25,6 +26,8 @@ We don't support building a static OpenRC with PAM.
 You may need to use PROGLDFLAGS=-Wl,-Bstatic on glibc instead of just -static.
 If you debug memory under valgrind, add -DDEBUG_MEMORY to your CPPFLAGS
 so that all malloc memory should be freed at exit.
+If you are building OpenRC for a Gentoo Prefix installation, add
+MKPREFIX=yes.
 
 You can also brand OpenRC if you so wish like so
 BRANDING=\"Gentoo/$(uname -s)\"
diff --git a/mk/os-prefix.mk b/mk/os-prefix.mk
new file mode 100644
index 00000000..94fda963
--- /dev/null
+++ b/mk/os-prefix.mk
@@ -0,0 +1,6 @@
+# Copyright (c) 2012 William Hubbs <w.d.hubbs@gmail.com>
+# Released under the 2-clause BSD license.
+
+ifeq (${MKPREFIX},yes}
+CPPFLAGS+=	-DPREFIX
+endif
diff --git a/mk/os.mk b/mk/os.mk
index c306f05f..3e189625 100644
--- a/mk/os.mk
+++ b/mk/os.mk
@@ -7,5 +7,6 @@ _OS_SH=		uname -s
 _OS:= 		$(shell ${_OS_SH})
 OS?= 		${_OS}
 include ${MK}/os-${OS}.mk
+include ${MK}/os-prefix.mk
 
 RC_LIB=		/$(LIBNAME)/rc