diff --git a/common.sh b/common.sh
index 340eddf694..58187de883 100644
--- a/common.sh
+++ b/common.sh
@@ -765,3 +765,14 @@ function emerge_custom_kernel() {
   sudo -E PKGDIR="${tmp_pkgdir}" $EMERGE_BOARD_CMD --usepkgonly \
     --root=${install_root} ${kernel} || die "Cannot emerge kernel to root"
 }
+
+function enable_strict_sudo {
+  if [ -z "$CROS_SUDO_KEEP_ALIVE" ]; then
+    echo "$0 was somehow invoked in a way that the sudo keep alive could"
+    echo "not be found.  Failing due to this.  See crosbug.com/18393."
+    exit 126
+  fi
+  function sudo {
+    `type -P sudo` -n "$@"
+  }
+}
diff --git a/sdk_lib/enter_chroot.sh b/sdk_lib/enter_chroot.sh
index 0339a761fe..de484afe48 100755
--- a/sdk_lib/enter_chroot.sh
+++ b/sdk_lib/enter_chroot.sh
@@ -9,6 +9,8 @@
 SCRIPT_ROOT=$(readlink -f $(dirname "$0")/..)
 . "${SCRIPT_ROOT}/common.sh" || exit 1
 
+enable_strict_sudo
+
 # Script must be run outside the chroot and as a regular user.
 assert_outside_chroot
 assert_not_root_user
diff --git a/sdk_lib/make_chroot.sh b/sdk_lib/make_chroot.sh
index 5479a0fc33..56f37e5cc8 100755
--- a/sdk_lib/make_chroot.sh
+++ b/sdk_lib/make_chroot.sh
@@ -14,6 +14,8 @@ SCRIPT_ROOT=$(readlink -f $(dirname "$0")/..)
 
 ENTER_CHROOT=$(readlink -f $(dirname "$0")/enter_chroot.sh)
 
+enable_strict_sudo
+
 # Check if the host machine architecture is supported.
 ARCHITECTURE="$(uname -m)"
 if [[ "$ARCHITECTURE" != "x86_64" ]]; then