diff --git a/zerver/lib/message.py b/zerver/lib/message.py
index 0e16d69bbc..dc5f89beae 100644
--- a/zerver/lib/message.py
+++ b/zerver/lib/message.py
@@ -730,7 +730,7 @@ def aggregate_streams(*, input_dict: dict[int, RawUnreadStreamDict]) -> list[Unr
     for message_id, attribute_dict in input_dict.items():
         stream_id = attribute_dict["stream_id"]
         topic_name = attribute_dict["topic"]
-        lookup_key = (stream_id, topic_name)
+        lookup_key = (stream_id, topic_name.lower())
         if lookup_key not in lookup_dict:
             obj = UnreadStreamInfo(
                 stream_id=stream_id,
diff --git a/zerver/tests/test_event_system.py b/zerver/tests/test_event_system.py
index f78eb99a82..fbb9366d34 100644
--- a/zerver/tests/test_event_system.py
+++ b/zerver/tests/test_event_system.py
@@ -17,7 +17,7 @@ from zerver.actions.presence import do_update_user_presence
 from zerver.actions.user_settings import do_change_user_setting
 from zerver.actions.users import do_change_user_role
 from zerver.lib.event_schema import check_web_reload_client_event
-from zerver.lib.events import fetch_initial_state_data
+from zerver.lib.events import fetch_initial_state_data, post_process_state
 from zerver.lib.exceptions import AccessDeniedError
 from zerver.lib.request import RequestVariableMissingError
 from zerver.lib.test_classes import ZulipTestCase
@@ -828,6 +828,22 @@ class FetchInitialStateDataTest(ZulipTestCase):
         [pronouns_field] = (field for field in custom_profile_fields if field["name"] == "Pronouns")
         self.assertEqual(pronouns_field["type"], CustomProfileField.PRONOUNS)
 
+    def test_unreads_case_insensitive_topics(self) -> None:
+        sender = self.example_user("hamlet")
+        self.login_user(sender)
+        self.send_stream_message(sender, "Denmark", "**hello**", topic_name="case DOES not MATTER")
+        self.send_stream_message(sender, "Denmark", "**bye**", topic_name="CASE does NOT matter")
+
+        reader = self.example_user("othello")
+        result = fetch_initial_state_data(
+            user_profile=reader,
+            realm=reader.realm,
+        )
+        post_process_state(reader, result, False)
+        self.assert_length(result["unread_msgs"]["streams"], 1)
+        self.assertEqual(result["unread_msgs"]["streams"][0]["topic"], "case DOES not MATTER")
+        self.assert_length(result["unread_msgs"]["streams"][0]["unread_message_ids"], 2)
+
 
 class ClientDescriptorsTest(ZulipTestCase):
     def test_get_client_info_for_all_public_streams(self) -> None: