--- /usr/portage/sys-apps/shadow/shadow-4.8.1-r1.ebuild	2020-02-07 10:31:43.598626105 +0100
+++ shadow-4.8.1-r1.ebuild	2020-02-09 12:29:53.763886545 +0100
@@ -12,7 +12,7 @@
 LICENSE="BSD GPL-2"
 SLOT="0"
 KEYWORDS="~alpha ~amd64 ~arm ~arm64 ~hppa ~ia64 ~m68k ~mips ~ppc ~ppc64 ~riscv ~s390 ~sh ~sparc ~x86"
-IUSE="acl audit bcrypt +cracklib nls pam selinux skey split-usr +su xattr"
+IUSE="acl audit bcrypt +btrfs +cracklib nls pam selinux skey split-usr +su xattr"
 # Taken from the man/Makefile.am file.
 LANGS=( cs da de es fi fr hu id it ja ko pl pt_BR ru sv tr zh_CN zh_TW )
 
@@ -55,7 +55,7 @@
 		--disable-account-tools-setuid
 		--enable-shared=no
 		--enable-static=yes
-		--with-btrfs
+		$(use_with btrfs)
 		--without-group-name-max-length
 		--without-tcb
 		$(use_enable nls)