diff --git a/backend/app/channels/slack.py b/backend/app/channels/slack.py
index 32b42e5a8..c9ad6a6ec 100644
--- a/backend/app/channels/slack.py
+++ b/backend/app/channels/slack.py
@@ -30,7 +30,7 @@ class SlackChannel(Channel):
         self._socket_client = None
         self._web_client = None
         self._loop: asyncio.AbstractEventLoop | None = None
-        self._allowed_users: set[str] = set(config.get("allowed_users", []))
+        self._allowed_users: set[str] = {str(user_id) for user_id in config.get("allowed_users", [])}
 
     async def start(self) -> None:
         if self._running:
diff --git a/backend/tests/test_channels.py b/backend/tests/test_channels.py
index 8e7546ded..aaa5997b9 100644
--- a/backend/tests/test_channels.py
+++ b/backend/tests/test_channels.py
@@ -7,7 +7,7 @@ import json
 import tempfile
 from pathlib import Path
 from types import SimpleNamespace
-from unittest.mock import AsyncMock, MagicMock
+from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
 
@@ -1988,6 +1988,47 @@ class TestSlackSendRetry:
 
         _run(go())
 
+
+class TestSlackAllowedUsers:
+    def test_numeric_allowed_users_match_string_event_user_id(self):
+        from app.channels.slack import SlackChannel
+
+        bus = MessageBus()
+        bus.publish_inbound = AsyncMock()
+        channel = SlackChannel(
+            bus=bus,
+            config={"allowed_users": [123456]},
+        )
+        channel._loop = MagicMock()
+        channel._loop.is_running.return_value = True
+        channel._add_reaction = MagicMock()
+        channel._send_running_reply = MagicMock()
+
+        event = {
+            "user": "123456",
+            "text": "hello from slack",
+            "channel": "C123",
+            "ts": "1710000000.000100",
+        }
+
+        def submit_coro(coro, loop):
+            coro.close()
+            return MagicMock()
+
+        with patch(
+            "app.channels.slack.asyncio.run_coroutine_threadsafe",
+            side_effect=submit_coro,
+        ) as submit:
+            channel._handle_message_event(event)
+
+        channel._add_reaction.assert_called_once_with("C123", "1710000000.000100", "eyes")
+        channel._send_running_reply.assert_called_once_with("C123", "1710000000.000100")
+        submit.assert_called_once()
+        inbound = bus.publish_inbound.call_args.args[0]
+        assert inbound.user_id == "123456"
+        assert inbound.chat_id == "C123"
+        assert inbound.text == "hello from slack"
+
     def test_raises_after_all_retries_exhausted(self):
         from app.channels.slack import SlackChannel