diff --git a/zerver/data_import/gitter.py b/zerver/data_import/gitter.py
index 5f93939e43..a86ea5f014 100644
--- a/zerver/data_import/gitter.py
+++ b/zerver/data_import/gitter.py
@@ -230,7 +230,7 @@ def convert_gitter_workspace_messages(
         get_user_from_message,
         get_timestamp_from_message,
         lambda id: user_map[id],
-        list(user_map.keys()),
+        iter(user_map.keys()),
         zerver_userprofile,
     )
 
diff --git a/zerver/data_import/import_util.py b/zerver/data_import/import_util.py
index 621dd41a4a..7fc05b5823 100644
--- a/zerver/data_import/import_util.py
+++ b/zerver/data_import/import_util.py
@@ -755,7 +755,7 @@ def long_term_idle_helper(
     user_from_message: Callable[[ZerverFieldsT], Optional[ExternalId]],
     timestamp_from_message: Callable[[ZerverFieldsT], float],
     zulip_user_id_from_user: Callable[[ExternalId], int],
-    all_user_ids: List[ExternalId],
+    all_user_ids_iterator: Iterator[ExternalId],
     zerver_userprofile: List[ZerverFieldsT],
 ) -> Set[int]:
     """Algorithmically, we treat users who have sent at least 10 messages
@@ -786,7 +786,7 @@ def long_term_idle_helper(
 
     long_term_idle = set()
 
-    for user_id in all_user_ids:
+    for user_id in all_user_ids_iterator:
         if user_id in recent_senders:
             continue
         zulip_user_id = zulip_user_id_from_user(user_id)
diff --git a/zerver/data_import/slack.py b/zerver/data_import/slack.py
index 19180c4c1b..fa51f94c73 100755
--- a/zerver/data_import/slack.py
+++ b/zerver/data_import/slack.py
@@ -650,7 +650,7 @@ def process_long_term_idle_users(
         get_message_sending_user,
         get_timestamp_from_message,
         lambda id: slack_user_id_to_zulip_user_id[id],
-        [user["id"] for user in users],
+        iter(user["id"] for user in users),
         zerver_userprofile,
     )