diff --git a/build_image b/build_image
index 8b7c7ec0b7..6d943c8e54 100755
--- a/build_image
+++ b/build_image
@@ -102,8 +102,6 @@ for arg in "$@"; do
   esac
 done
 
-BASE_PACKAGE="coreos-base/coreos"
-
 eclean-$BOARD -d packages
 
 if [[ ${skip_blacklist_check} -ne 1 ]]; then
@@ -139,14 +137,12 @@ mkdir -p "${BUILD_DIR}"
 DISK_LAYOUT="${FLAGS_disk_layout:-base}"
 
 if [[ "${DEV_IMAGE}" -eq 1 ]]; then
-  create_base_image ${COREOS_DEVELOPER_IMAGE_NAME} ${DISK_LAYOUT} ${FLAGS_group}
-  install_dev_packages ${COREOS_DEVELOPER_IMAGE_NAME} ${DISK_LAYOUT}
+  create_dev_image ${COREOS_DEVELOPER_IMAGE_NAME} ${DISK_LAYOUT} ${FLAGS_group}
   upload_image "${BUILD_DIR}/${COREOS_DEVELOPER_IMAGE_NAME}"
 fi
 
 if [[ "${PROD_IMAGE}" -eq 1 ]]; then
-  create_base_image ${COREOS_PRODUCTION_IMAGE_NAME} ${DISK_LAYOUT} ${FLAGS_group}
-  setup_prod_image ${COREOS_PRODUCTION_IMAGE_NAME} ${DISK_LAYOUT}
+  create_prod_image ${COREOS_PRODUCTION_IMAGE_NAME} ${DISK_LAYOUT} ${FLAGS_group}
   upload_image "${BUILD_DIR}/${COREOS_PRODUCTION_IMAGE_NAME}"
   if [[ ${FLAGS_generate_update} -eq ${FLAGS_TRUE} ]]; then
     generate_update "${COREOS_PRODUCTION_IMAGE_NAME}" ${DISK_LAYOUT}
diff --git a/build_library/base_image_util.sh b/build_library/base_image_util.sh
index b90312d738..e4bf81d078 100755
--- a/build_library/base_image_util.sh
+++ b/build_library/base_image_util.sh
@@ -2,13 +2,12 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-create_base_image() {
+start_image() {
   local image_name=$1
   local disk_layout=$2
-  local update_group="$3"
+  local root_fs_dir=$3
 
   local disk_img="${BUILD_DIR}/${image_name}"
-  local root_fs_dir="${BUILD_DIR}/rootfs"
 
   info "Using image type ${disk_layout}"
   "${BUILD_LIBRARY_DIR}/disk_util" --disk_layout="${disk_layout}" \
@@ -26,16 +25,12 @@ create_base_image() {
   # FIXME(marineam): Work around glibc setting EROOT=$ROOT
   # https://bugs.gentoo.org/show_bug.cgi?id=473728#c12
   sudo mkdir -p "${root_fs_dir}/etc/ld.so.conf.d"
+}
 
-  # We "emerge --root=${root_fs_dir} --root-deps=rdeps --usepkgonly" all of the
-  # runtime packages for chrome os. This builds up a chrome os image from
-  # binary packages with runtime dependencies only.  We use INSTALL_MASK to
-  # trim the image size as much as possible.
-  emerge_prod_gcc --root="${root_fs_dir}"
-  emerge_to_image --root="${root_fs_dir}" ${BASE_PACKAGE}
-
-  # Make sure profile.env and ld.so.cache has been generated
-  sudo ROOT="${root_fs_dir}" env-update
+finish_image() {
+  local disk_layout=$1
+  local root_fs_dir=$2
+  local update_group=$3
 
   # Record directories installed to the state partition.
   # Explicitly ignore entries covered by existing configs.
diff --git a/build_library/build_image_util.sh b/build_library/build_image_util.sh
index 1122799801..a7a7201176 100755
--- a/build_library/build_image_util.sh
+++ b/build_library/build_image_util.sh
@@ -107,6 +107,7 @@ generate_update() {
 # Arguments to this command are passed as addition options/arguments
 # to the basic emerge command.
 emerge_to_image() {
+  local root_fs_dir="$1"; shift
   local mask="${INSTALL_MASK:-$(portageq-$BOARD envvar PROD_INSTALL_MASK)}"
   test -n "$mask" || die "PROD_INSTALL_MASK not defined"
 
@@ -122,12 +123,16 @@ emerge_to_image() {
     emerge_cmd+=" --jobs=$FLAGS_jobs"
   fi
 
-  sudo -E INSTALL_MASK="$mask" ${emerge_cmd} "$@"
+  sudo -E INSTALL_MASK="$mask" ${emerge_cmd} --root="${root_fs_dir}" "$@"
+
+  # Make sure profile.env and ld.so.cache has been generated
+  sudo -E ROOT="${root_fs_dir}" env-update
 }
 
 # The GCC package includes both its libraries and the compiler.
 # In prod images we only need the shared libraries.
 emerge_prod_gcc() {
+    local root_fs_dir="$1"; shift
     local mask="${INSTALL_MASK:-$(portageq-$BOARD envvar PROD_INSTALL_MASK)}"
     test -n "$mask" || die "PROD_INSTALL_MASK not defined"
 
@@ -143,5 +148,5 @@ emerge_prod_gcc() {
         /usr/share/gcc-data/*/*/c99
         /usr/share/gcc-data/*/*/python"
 
-    INSTALL_MASK="${mask}" emerge_to_image --nodeps sys-devel/gcc "$@"
+    INSTALL_MASK="${mask}" emerge_to_image "${root_fs_dir}" --nodeps sys-devel/gcc "$@"
 }
diff --git a/build_library/dev_image_util.sh b/build_library/dev_image_util.sh
index 6b8f63a5d4..cc376d8d85 100755
--- a/build_library/dev_image_util.sh
+++ b/build_library/dev_image_util.sh
@@ -50,11 +50,10 @@ detect_dev_url() {
     fi
 }
 
-# Modifies an existing image to add development packages.
-# Takes as an arg the name of the image to be created.
-install_dev_packages() {
+create_dev_image() {
   local image_name=$1
   local disk_layout=$2
+  local update_group=$3
   local devserver=$(detect_dev_url)
   local auserver=""
 
@@ -65,18 +64,16 @@ install_dev_packages() {
     info "Unable do detect local dev server address."
   fi
 
-  info "Adding developer packages to ${image_name}"
+  info "Building developer image ${image_name}"
   local root_fs_dir="${BUILD_DIR}/rootfs"
 
-  "${BUILD_LIBRARY_DIR}/disk_util" --disk_layout="${disk_layout}" \
-      mount "${BUILD_DIR}/${image_name}" "${root_fs_dir}"
-  trap "cleanup_mounts '${root_fs_dir}' && delete_prompt" EXIT
+  start_image "${image_name}" "${disk_layout}" "${root_fs_dir}"
 
-  # Install developer packages described in coreos-dev.
-  emerge_to_image --root="${root_fs_dir}" coreos-base/coreos-dev
+  emerge_to_image "${root_fs_dir}" coreos-base/coreos-dev
 
-  # Make sure profile.env and ld.so.cache has been generated
-  sudo ROOT="${root_fs_dir}" env-update
+  "${BUILD_LIBRARY_DIR}/set_lsb_release" \
+    --root="${root_fs_dir}" \
+    --board="${BOARD}"
 
   # Setup portage for emerge and gmerge
   configure_dev_portage "${root_fs_dir}" "${devserver}"
@@ -101,12 +98,5 @@ EOF
   sudo mkdir -p "${fs_wants}"
   sudo ln -s ../remount-usr.service "${fs_wants}"
 
-  # Zero all fs free space, not fatal since it won't work on linux < 3.2
-  sudo fstrim "${root_fs_dir}" || true
-  sudo fstrim "${root_fs_dir}/usr" || true
-
-  info "Developer image built and stored at ${image_name}"
-
-  cleanup_mounts "${root_fs_dir}"
-  trap - EXIT
+  finish_image "${disk_layout}" "${root_fs_dir}" "${update_group}"
 }
diff --git a/build_library/prod_image_util.sh b/build_library/prod_image_util.sh
index 66b1a44662..3e4f492d9c 100755
--- a/build_library/prod_image_util.sh
+++ b/build_library/prod_image_util.sh
@@ -3,16 +3,19 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-setup_prod_image() {
+create_prod_image() {
   local image_name="$1"
   local disk_layout="$2"
+  local update_group="$3"
 
-  info "Configuring production image ${image_name}"
+  info "Building production image ${image_name}"
   local root_fs_dir="${BUILD_DIR}/rootfs"
 
-  "${BUILD_LIBRARY_DIR}/disk_util" --disk_layout="${disk_layout}" \
-      mount "${BUILD_DIR}/${image_name}" "${root_fs_dir}"
-  trap "cleanup_mounts '${root_fs_dir}' && delete_prompt" EXIT
+  start_image "${image_name}" "${disk_layout}" "${root_fs_dir}"
+
+  # Install minimal GCC (libs only) and then everything else
+  emerge_prod_gcc "${root_fs_dir}"
+  emerge_to_image "${root_fs_dir}" coreos-base/coreos
 
   # clean-ups of things we do not need
   sudo rm ${root_fs_dir}/etc/csh.env
@@ -38,8 +41,7 @@ EOF
   sudo rm ${root_fs_dir}/etc/xinetd.d/rsyncd
   sudo rmdir ${root_fs_dir}/etc/xinetd.d
 
-  cleanup_mounts "${root_fs_dir}"
-  trap - EXIT
+  finish_image "${disk_layout}" "${root_fs_dir}" "${update_group}"
 
   # Make the filesystem un-mountable as read-write.
   if [ ${FLAGS_enable_rootfs_verification} -eq ${FLAGS_TRUE} ]; then