diff --git a/mailman_sync.py b/mailman_sync.py
index 18c0113..d9a602f 100755
--- a/mailman_sync.py
+++ b/mailman_sync.py
@@ -64,7 +64,7 @@ def config_list(
 
 # TODO: this will never update someone's display name
 def diff_roster(
-    expected_members: list[str], existing_members: list[mailmanclient.Member]
+    expected_members: set[str], existing_members: set[mailmanclient.Member]
 ) -> tuple[dict[str, str], list[mailmanclient.Member]]:
     expected_members_dict = dict(
         list(reversed(email.utils.parseaddr(member))) for member in expected_members
@@ -82,9 +82,9 @@ def diff_roster(
 
 
 def sync_members(
-    list: mailmanclient.MailingList, dry_run: bool, expected_members: list[str]
+    list: mailmanclient.MailingList, dry_run: bool, expected_members: set[str]
 ):
-    members_to_add, members_to_remove = diff_roster(expected_members, list.members)
+    members_to_add, members_to_remove = diff_roster(expected_members, set(list.members))
 
     for address, display_name in members_to_add.items():
         print(f"Adding '{display_name} <{address}>' to list {list}")
@@ -106,9 +106,11 @@ def sync_members(
 
 
 def sync_moderators(
-    list: mailmanclient.MailingList, dry_run: bool, expected_members: list[str]
+    list: mailmanclient.MailingList, dry_run: bool, expected_members: set[str]
 ):
-    members_to_add, members_to_remove = diff_roster(expected_members, list.moderators)
+    members_to_add, members_to_remove = diff_roster(
+        expected_members, set(list.moderators)
+    )
 
     for address, display_name in members_to_add.items():
         print(f"Adding '{display_name} <{address}>' as moderator to list {list}")
@@ -197,8 +199,8 @@ def main(
             config_list(list, dry_run, **props["config"])
 
         if "moderators" in props:
-            sync_moderators(list, dry_run, props["moderators"])
-        sync_members(list, dry_run, props["members"])
+            sync_moderators(list, dry_run, set(props["moderators"]))
+        sync_members(list, dry_run, set(props["members"]) | set(props["moderators"]))
 
     lists = [list.list_name.lower() for list in domain.get_lists()]
     update_cloudflare_lists(