diff --git a/lxc-build b/lxc-build
index 63d2ebd..bdfc682 100755
--- a/lxc-build
+++ b/lxc-build
@@ -93,7 +93,7 @@ class LXCImage:
             rootfs_path = self.layers[0]
         else:
             # Multiple lower overlayfs layers are ordered from right to left (lower2:lower1:rootfs:upper)
-            rootfs_path = 'overlay:{}:{}'.format(':'.join(self.layers[:-1][::-1], self.layers[-1]))
+            rootfs_path = 'overlay:{}:{}'.format(':'.join(self.layers[:-1][::-1]), self.layers[-1])
         mount_entries = '\n'.join(['lxc.mount.entry = {} none bind 0 0'.format(m) for m in self.mounts])
         with open(os.path.join(LXC_ROOT, self.name, 'config'), 'w') as fd:
             fd.write(CONFIG_TEMPLATE.format(name=self.name, rootfs=rootfs_path, mounts=mount_entries, uid=self.uid, gid=self.gid, cmd=self.cmd))
@@ -122,7 +122,7 @@ class LXCImage:
         copy_tree(src, dst)
 
     def add_mount(self, src, dst):
-        mounts.append('{} {}'.format(src, dst))
+        self.mounts.append('{} {}'.format(src, dst))
         self.rebuild_config()
 
     def set_user(self, uid, gid):