diff --git a/elements/ubuntu/root.d/10-cache-ubuntu-tarball b/elements/ubuntu/root.d/10-cache-ubuntu-tarball
index cb2159dc..e3d41129 100755
--- a/elements/ubuntu/root.d/10-cache-ubuntu-tarball
+++ b/elements/ubuntu/root.d/10-cache-ubuntu-tarball
@@ -1,7 +1,7 @@
 #!/bin/bash
 # These are useful, or at worst not harmful, for all images we build.
 
-set -e
+set -eu
 
 [ -n "$ARCH" ]
 [ -n "$TARGET_ROOT" ]
@@ -13,13 +13,18 @@ DIB_CLOUD_IMAGES=${DIB_CLOUD_IMAGES:-http://cloud-images.ubuntu.com/}
 DIB_RELEASE=${DIB_RELEASE:-quantal}
 BASE_IMAGE_FILE=${BASE_IMAGE_FILE:-$DIB_RELEASE-server-cloudimg-$ARCH-root.tar.gz}
 SHA256SUMS=${SHA256SUMS:-https://${DIB_CLOUD_IMAGES##http?(s)://}/$DIB_RELEASE/current/SHA256SUMS}
+CACHED_FILE=$IMG_PATH/$BASE_IMAGE_FILE
 
-echo "Fetching Base Image"
-$TMP_HOOKS_PATH/bin/cache-url $SHA256SUMS $IMG_PATH/SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH
-$TMP_HOOKS_PATH/bin/cache-url $DIB_CLOUD_IMAGES/$DIB_RELEASE/current/$BASE_IMAGE_FILE $IMG_PATH/$BASE_IMAGE_FILE
-pushd $IMG_PATH
-grep "$BASE_IMAGE_FILE" SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH | sha256sum --check -
-popd
+if [ -n "$DIB_OFFLINE" -a -f "$CACHED_FILE" ] ; then
+    echo "Not checking freshness of cached $CACHED_FILE."
+else
+  echo "Fetching Base Image"
+  $TMP_HOOKS_PATH/bin/cache-url $SHA256SUMS $IMG_PATH/SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH
+  $TMP_HOOKS_PATH/bin/cache-url $DIB_CLOUD_IMAGES/$DIB_RELEASE/current/$BASE_IMAGE_FILE $CACHED_FILE
+  pushd $IMG_PATH
+  grep "$BASE_IMAGE_FILE" SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH | sha256sum --check -
+  popd
+fi
 # Extract the base image
 sudo tar -C $TARGET_ROOT -xzf $IMG_PATH/$BASE_IMAGE_FILE
 sudo rmdir $TARGET_ROOT/lost+found