diff --git a/scale_build/image/bootstrap.py b/scale_build/image/bootstrap.py
index 92079ea..805c031 100644
--- a/scale_build/image/bootstrap.py
+++ b/scale_build/image/bootstrap.py
@@ -36,6 +36,8 @@ def umount_chroot_basedir():
     for command in (
         ['umount', '-f', PACKAGE_PATH],
         ['umount', '-f', os.path.join(CHROOT_BASEDIR, 'proc')],
+        # Need to unmount efivarfs before sys (automatically mounted under sys)
+        ['umount', '-f', os.path.join(CHROOT_BASEDIR, 'sys/firmware/efi/efivars')],
         ['umount', '-f', os.path.join(CHROOT_BASEDIR, 'sys')],
     ):
         run(command, check=False, log=False)