diff --git a/bin/cros_update_image.sh b/bin/cros_update_image.sh
index 4ffe59ec1f..ebca9fbf83 100755
--- a/bin/cros_update_image.sh
+++ b/bin/cros_update_image.sh
@@ -66,10 +66,10 @@ if [[ ${PKGS/kernel/} != ${PKGS} ]]; then
    sudo dd if="./rootfs/boot/vmlinuz" of=part_2 bs=512 count=8192 conv=notrunc
 fi
 
-sudo umount rootfs/usr/local
-sudo umount rootfs/var
-sudo umount rootfs
-sudo umount stateful_part
+safe_umount rootfs/usr/local
+safe_umount rootfs/var
+safe_umount rootfs
+safe_umount stateful_part
 ./pack_partitions.sh ${IMAGE}
 
 cd -
diff --git a/build_library/disk_layout_util.sh b/build_library/disk_layout_util.sh
index 29ce67cd85..e75c07dac2 100644
--- a/build_library/disk_layout_util.sh
+++ b/build_library/disk_layout_util.sh
@@ -64,7 +64,7 @@ run_partition_script() {
   sudo mount -o loop "${root_fs_img}" "${root_fs_dir}"
   . "${root_fs_dir}/${PARTITION_SCRIPT_PATH}"
   write_partition_table "${outdev}" "${pmbr_img}"
-  sudo umount "${root_fs_dir}"
+  safe_umount "${root_fs_dir}"
 }
 
 get_fs_block_size() {
diff --git a/common.sh b/common.sh
index 78a0cc3f8b..7693d6ea84 100644
--- a/common.sh
+++ b/common.sh
@@ -705,7 +705,33 @@ safe_umount_tree() {
 
 # Run umount as root.
 safe_umount() {
-  $([[ ${UID:-$(id -u)} != 0 ]] && echo sudo) umount "$@"
+  local ret=0
+  local out=""
+  set +e
+  for i in $(seq 1 4); do
+    out=`$([[ ${UID:-$(id -u)} != 0 ]] && echo sudo) umount "$@" 2>&1`
+    ret=$?
+    if [[ $ret -eq 0 ]]; then
+      set -e
+      return 0
+    fi
+    # Mount is not found
+    if [[ `expr index "${out}" "not found"` -ne "0" ]]; then
+      set -e
+      return 0
+    fi
+    # Mount is not mounted.
+    if [[ `expr index "${out}" "not mounted"` -ne "0" ]]; then
+      set -e
+      return 0
+    fi
+    sleep 1
+    # Mount is actually busy.
+    if [[ `expr index "${out}" "busy"` -ne "0" ]]; then
+      continue
+    fi
+  done
+  return $ret
 }
 
 get_git_id() {