diff --git a/certbot/tests/compat/os_test.py b/certbot/tests/compat/os_test.py
new file mode 100644
index 000000000..0a1080cbc
--- /dev/null
+++ b/certbot/tests/compat/os_test.py
@@ -0,0 +1,10 @@
+import unittest
+
+from certbot.compat import os
+
+
+class OsTest(unittest.TestCase):
+    """Unit tests for os module."""
+    def test_forbidden_methods(self):
+        for method in ['chmod']:
+            self.assertRaises(RuntimeError, getattr(os, method))