diff --git a/tools/testing/selftests/damon/_damon_sysfs.py b/tools/testing/selftests/damon/_damon_sysfs.py
index e98cf4b6a4b7..f9fead3d0f01 100644
--- a/tools/testing/selftests/damon/_damon_sysfs.py
+++ b/tools/testing/selftests/damon/_damon_sysfs.py
@@ -241,6 +241,8 @@ class DamonCtx:
         nr_schemes_file = os.path.join(
                 self.sysfs_dir(), 'schemes', 'nr_schemes')
         content, err = read_file(nr_schemes_file)
+        if err is not None:
+            return err
         if int(content) != len(self.schemes):
             err = write_file(nr_schemes_file, '%d' % len(self.schemes))
             if err != None: