diff --git a/client/image.py b/client/image.py
index 0bcb75c..b8c83bc 100755
--- a/client/image.py
+++ b/client/image.py
@@ -142,12 +142,10 @@ class Imager(object):
         FLAGS.https_client_cert,
         FLAGS.https_client_key)
 
-  def _UpdateGrub(self, root, image_dir):
-    boot_dir = os.path.join(root, 'isodevice')
-
+  def _UpdateGrub(self, image_dir, root):
     update = update_grub.GrubUpdater(
         image_dir,
-        boot_dir)
+        root)
     update.Update()
 
   def _FetchImages(self, root):
@@ -164,7 +162,7 @@ class Imager(object):
     root = self._MountBoot()
     self._InstallGrub(root)
     image_dir = self._FetchImages(root)
-    self._UpdateGrub(root, image_dir)
+    self._UpdateGrub(image_dir, root)
 
   def Image(self):
     self._umount = []
diff --git a/client/update_grub.py b/client/update_grub.py
index 13d193f..7dae468 100755
--- a/client/update_grub.py
+++ b/client/update_grub.py
@@ -14,7 +14,7 @@ class GrubUpdater(object):
     self._image_dir = image_dir
     self._boot_dir = boot_dir
 
-    assert self._image_dir.startswith(self._boot_dir)
+    assert self._image_dir.startswith(self._boot_dir), (self._image_dir, self._boot_dir)
 
     self._image_path = '/' + os.path.relpath(self._image_dir, self._boot_dir)