diff --git a/etc/build.usage b/etc/build.usage
index 6993ed7..c68dc4c 100644
--- a/etc/build.usage
+++ b/etc/build.usage
@@ -9,18 +9,21 @@ usage: ./build.sh [-x] [-4|6] [-a nt32|nt64] [-b debug|release] [-c] [-h]
         -h                      Show this screen.
         -i                      Ignore SHA256 hash mismatches when downloading files.
         -N                      Offline mode: no {wget,git-{clone,pull}}(1) calls.
-        -r package[,...][:step] Restart the specified comma-separated build(s) completely or at
-                                the optionally specified step. Currently defined steps are:
-                                fetch_wget, fetch_git, fetch_extract, configure_patch_pre,
-                                configure_autotools, configure_patch, configure, build_clean,
-                                build, install_subdirs, install_make, install_files, install_libs,
-                                install_pkgconfig, install_purge_la, install_strip, and install.
+        -r package[,...][:step] Restart the specified comma-separated build(s) completely
+                                or at the optionally specified step. Currently defined
+                                steps are:
+                                setup_distclean, fetch_wget, fetch_git, fetch_extract,
+                                configure_patch_pre, configure_autotools, configure_patch,
+                                configure, build_clean, build, install_subdirs, install_make,
+                                install_files, install_libs, install_pkgconfig, install_purge_la,
+                                install_strip, and install.
         -R                      Ignore build failures and continue building (relaxed mode.)
-        -t[.gz|.bz2|.xz]        Produce binary distribution and source tarballs containing ${PREFIX}
-                                sans ${WORKDIR} and ${PREFIX}/src/midipix_build and ${WORKDIR} sans top-
-                                level regular files at the end of a build with zero failures. The
-                                tarballs will be compressed with either gzip, bzip2, or xz and signed
-                                with GPG; the default compression is xz.
+        -t[.gz|.bz2|.xz]        Produce binary distribution and source tarballs containing
+                                ${PREFIX} sans ${WORKDIR} and ${PREFIX}/src/midipix_build
+                                and ${WORKDIR} sans top-level regular files at the end of
+                                a build with zero failures. The tarballs will be compressed
+                                with either gzip, bzip2, or xz and signed with GPG; the
+                                default compression is xz.
         -v                      Be verbose.
         --debug-minipix         Don't strip(1) minipix binaries to facilitate debugging minipix.
         <target>[ ...]          One of:
diff --git a/subr/pkg_setup_distclean.subr b/subr/pkg_setup_distclean.subr
new file mode 100644
index 0000000..fc5999c
--- /dev/null
+++ b/subr/pkg_setup_distclean.subr
@@ -0,0 +1,12 @@
+#
+# set -o errexit -o noglob are assumed.
+#
+
+pkg_setup_distclean() {
+	if [ "$(stat -c %i "${PKG_BASE_DIR}")"	\
+	!=   "$(stat -c %i "${WORKDIR}")" ]; then
+		build_fileop rm "${PKG_BASE_DIR}";
+	fi;
+};
+
+# vim:filetype=sh
diff --git a/subr/pkg_setup_env.subr b/subr/pkg_setup_env.subr
index a02b1a6..f6d6118 100644
--- a/subr/pkg_setup_env.subr
+++ b/subr/pkg_setup_env.subr
@@ -53,8 +53,6 @@ pkg_setup_env() {
 		PKG_ENV_VARS="$(echo "${PKG_ENV_VARS}" | tr " " "\n" | sort | tr "\n" " ")";
 		log_env_vars "build" ${PKG_ENV_VARS};
 	fi;
-	build_fileop mkdir "${PKG_BASE_DIR}";
-	build_fileop cd "${PKG_BASE_DIR}";
 };
 
 # vim:filetype=sh
diff --git a/subr/pkg_setup_subdirs.subr b/subr/pkg_setup_subdirs.subr
new file mode 100644
index 0000000..1fc279c
--- /dev/null
+++ b/subr/pkg_setup_subdirs.subr
@@ -0,0 +1,10 @@
+#
+# set -o errexit -o noglob are assumed.
+#
+
+pkg_setup_subdirs() {
+	build_fileop mkdir "${PKG_BASE_DIR}";
+	build_fileop cd "${PKG_BASE_DIR}";
+};
+
+# vim:filetype=sh
diff --git a/vars/env.vars b/vars/env.vars
index afbff05..6f184cc 100644
--- a/vars/env.vars
+++ b/vars/env.vars
@@ -16,7 +16,8 @@
 : ${PREFIX_CROSS:=${PREFIX}/${TARGET}};
 : ${DLCACHEDIR:=${PREFIX_ROOT}/dlcache};
 : ${WORKDIR:=${PREFIX}/tmp};
-: ${BUILD_STEPS:="setup_vars:invariant setup_env:invariant all:all
+: ${BUILD_STEPS:="setup_vars:invariant setup_env:invariant setup_distclean:variant setup_subdirs:invariant
+	all:all
 	fetch_wget:dynamic fetch_git:dynamic fetch_extract:dynamic fetch_subdirs:invariant fetch:virtual
 	configure_patch_pre:dynamic configure_autotools:dynamic configure_patch:dynamic configure:dynamic
 	build_clean:variant build:dynamic