diff --git a/certbot-postfix/certbot_postfix/installer.py b/certbot-postfix/certbot_postfix/installer.py
index 649e56c6b..d89847aef 100644
--- a/certbot-postfix/certbot_postfix/installer.py
+++ b/certbot-postfix/certbot_postfix/installer.py
@@ -59,9 +59,9 @@ class Installer(plugins_common.Installer):
         self.postconf = None
 
         # Files to save
-        self.save_notes = []
+        self.save_notes = [] # type: List[str]
 
-        self._enhance_func = {}
+        self._enhance_func = {} # type: Dict[str, Callable[[str, str]]]
         # Since we only need to enable TLS once for all domains,
         # keep track of whether this enhancement was already called.
         self._tls_enabled = False
diff --git a/certbot-postfix/certbot_postfix/postconf.py b/certbot-postfix/certbot_postfix/postconf.py
index 8248468ee..9d38a89ff 100644
--- a/certbot-postfix/certbot_postfix/postconf.py
+++ b/certbot-postfix/certbot_postfix/postconf.py
@@ -13,14 +13,14 @@ class ConfigMain(util.PostfixUtilBase):
         # Whether to ignore overrides from master.
         self._ignore_master_overrides = ignore_master_overrides
         # List of all current Postfix parameters, from `postconf` command.
-        self._db = {}
+        self._db = {} # type: Dict[str, str]
         # List of current master.cf overrides from Postfix config. Dictionary
         # of parameter name => list of tuples (service name, paramter value)
         # Note: We should never modify master without explicit permission.
-        self._master_db = {}
+        self._master_db = {} # Dict[str, List[Tuple[str, str]]]
         # List of all changes requested to the Postfix parameters as they are now
         # in _db. These changes are flushed to `postconf` on `flush`.
-        self._updated = {}
+        self._updated = {} # type: Dict[str, str]
         self._read_from_conf()
 
     def _read_from_conf(self):
diff --git a/certbot-postfix/certbot_postfix/tests/installer_test.py b/certbot-postfix/certbot_postfix/tests/installer_test.py
index 8243832ff..a4cf69c3c 100644
--- a/certbot-postfix/certbot_postfix/tests/installer_test.py
+++ b/certbot-postfix/certbot_postfix/tests/installer_test.py
@@ -158,6 +158,14 @@ class InstallerTest(certbot_test_util.ConfigTestCase):
                                               installer.prepare)
             certbot_test_util.lock_and_call(assert_raises, self.tempdir)
 
+
+    @mock.patch('certbot.util.lock_dir_until_exit')
+    def test_dir_locked(self, lock_dir):
+        with create_installer(self.config) as installer:
+            lock_dir.side_effect = errors.LockError
+            self.assertRaises(errors.PluginError, installer.prepare)
+        
+
     def test_more_info(self):
         with create_installer(self.config) as installer:
             installer.prepare()
@@ -288,7 +296,6 @@ def create_installer(config, main_cf=DEFAULT_MAIN_CF):
     from certbot_postfix import installer
     def _mock_init_postconf(postconf, executable, ignore_master_overrides=False, config_dir=None):
         # pylint: disable=protected-access
-        super(ConfigMain, postconf).__init__(executable, config_dir)
         postconf._ignore_master_overrides = ignore_master_overrides
         postconf._db = main_cf
         postconf._master_db = {}
diff --git a/certbot-postfix/certbot_postfix/tests/util_test.py b/certbot-postfix/certbot_postfix/tests/util_test.py
index 8673538a7..2ff8bf6d9 100644
--- a/certbot-postfix/certbot_postfix/tests/util_test.py
+++ b/certbot-postfix/certbot_postfix/tests/util_test.py
@@ -51,12 +51,12 @@ class PostfixUtilTest(unittest.TestCase):
         self.mock_call.assert_called_with(['check'])
 
     def test_test_raises_error_when_check_fails(self):
-        self.mock_call.side_effect = [subprocess.CalledProcessError(None, None, None)]
+        self.mock_call.side_effect = [subprocess.CalledProcessError(1, "")]
         self.assertRaises(errors.MisconfigurationError, self.postfix.test)
         self.mock_call.assert_called_with(['check'])
 
     def test_restart_while_running(self):
-        self.mock_call.side_effect = [subprocess.CalledProcessError(None, None, None), None]
+        self.mock_call.side_effect = [subprocess.CalledProcessError(1, ""), None]
         self.postfix.restart()
         self.mock_call.assert_called_with(['start'])
 
@@ -65,14 +65,14 @@ class PostfixUtilTest(unittest.TestCase):
         self.mock_call.assert_called_with(['reload'])
 
     def test_restart_raises_error_when_reload_fails(self):
-        self.mock_call.side_effect = [None, subprocess.CalledProcessError(None, None, None)]
+        self.mock_call.side_effect = [None, subprocess.CalledProcessError(1, "")]
         self.assertRaises(errors.PluginError, self.postfix.restart)
         self.mock_call.assert_called_with(['reload'])
 
     def test_restart_raises_error_when_start_fails(self):
         self.mock_call.side_effect = [
-             subprocess.CalledProcessError(None, None, None),
-             subprocess.CalledProcessError(None, None, None)]
+             subprocess.CalledProcessError(1, ""),
+             subprocess.CalledProcessError(1, "")]
         self.assertRaises(errors.PluginError, self.postfix.restart)
         self.mock_call.assert_called_with(['start'])