diff --git a/certbot/hooks.py b/certbot/hooks.py
index ae190a930..a8099c4a8 100644
--- a/certbot/hooks.py
+++ b/certbot/hooks.py
@@ -54,11 +54,11 @@ def pre_hook(config):
     if cmd and cmd not in pre_hook.already:
         logger.info("Running pre-hook command: %s", cmd)
         _run_hook(cmd)
-        pre_hook.already[cmd] = True
+        pre_hook.already.add(cmd)
     elif cmd:
         logger.info("Pre-hook command already run, skipping: %s", cmd)
 
-pre_hook.already = {}
+pre_hook.already = set()
 
 
 def post_hook(config):
diff --git a/certbot/tests/hook_test.py b/certbot/tests/hook_test.py
index a8f49745b..3165a67fc 100644
--- a/certbot/tests/hook_test.py
+++ b/certbot/tests/hook_test.py
@@ -47,7 +47,7 @@ class HookTest(unittest.TestCase):
             return mock_logger.warning
 
     def test_pre_hook(self):
-        hooks.pre_hook.already = {}
+        hooks.pre_hook.already = set()
         config = mock.MagicMock(pre_hook="true")
         self._test_a_hook(config, hooks.pre_hook, 1)
         self._test_a_hook(config, hooks.pre_hook, 0)