diff --git a/lets_do_dns/acme_dns_auth/authenticate.py b/lets_do_dns/acme_dns_auth/authenticate.py
index 7e915af..48be60d 100644
--- a/lets_do_dns/acme_dns_auth/authenticate.py
+++ b/lets_do_dns/acme_dns_auth/authenticate.py
@@ -41,9 +41,8 @@ def _run_post_cmd(self):
         if self._env.post_cmd:
             run(self._env.post_cmd,
                 env={'CERTBOT_HOSTNAME': self._env.fqdn,
-                     'PATH': ["/bin", "/sbin",
-                              "/usr/bin", "/usr/sbin",
-                              "/usr/local/bin", "/usr/local/sbin"]})
+                     'PATH': ("/bin:/sbin:/usr/bin:/usr/sbin:"
+                              "/usr/local/bin:/usr/local/sbin")})
 
     def _create_resource(self):
         self._resource.create()
diff --git a/tests/unit/acme_dns_auth/authenticate/test_cleanup_stage.py b/tests/unit/acme_dns_auth/authenticate/test_cleanup_stage.py
index 3601713..a8c772a 100644
--- a/tests/unit/acme_dns_auth/authenticate/test_cleanup_stage.py
+++ b/tests/unit/acme_dns_auth/authenticate/test_cleanup_stage.py
@@ -75,6 +75,5 @@ def test_passes_postcmd_to_run(mocker, fqdn):
     mock_run.assert_called_once_with(
         'test-program --help',
         env={'CERTBOT_HOSTNAME': fqdn,
-             'PATH': ["/bin", "/sbin",
-                      "/usr/bin", "/usr/sbin",
-                      "/usr/local/bin", "/usr/local/sbin"]})
+             'PATH': ("/bin:/sbin:/usr/bin:/usr/sbin:"
+                      "/usr/local/bin:/usr/local/sbin")})