diff --git a/matrix_webhook/utils.py b/matrix_webhook/utils.py
index 339472b..4c7917a 100644
--- a/matrix_webhook/utils.py
+++ b/matrix_webhook/utils.py
@@ -15,6 +15,13 @@ LOGGER = logging.getLogger("matrix_webhook.utils")
 CLIENT = AsyncClient(conf.MATRIX_URL, conf.MATRIX_ID)
 
 
+def error_map(resp):
+    """Map response errors to HTTP status."""
+    if resp.status_code == "M_UNKNOWN":
+        return resp.transport_response.status
+    return ERROR_MAP[resp.status_code]
+
+
 def create_json_response(status, ret):
     """Create a JSON response."""
     LOGGER.debug(f"Creating json response: {status=}, {ret=}")
@@ -34,9 +41,7 @@ async def join_room(room_id):
                     LOGGER.warning("Reconnecting")
                     await CLIENT.login(conf.MATRIX_PW)
                 else:
-                    return create_json_response(
-                        ERROR_MAP[resp.status_code], resp.message
-                    )
+                    return create_json_response(error_map(resp), resp.message)
             else:
                 return None
         except LocalProtocolError as e:
@@ -59,9 +64,7 @@ async def send_room_message(room_id, content):
                     LOGGER.warning("Reconnecting")
                     await CLIENT.login(conf.MATRIX_PW)
                 else:
-                    return create_json_response(
-                        ERROR_MAP[resp.status_code], resp.message
-                    )
+                    return create_json_response(error_map(resp), resp.message)
             else:
                 return create_json_response(HTTPStatus.OK, "OK")
         except LocalProtocolError as e:
diff --git a/tests/tests.py b/tests/tests.py
index aa5991c..7d44d7e 100644
--- a/tests/tests.py
+++ b/tests/tests.py
@@ -33,11 +33,11 @@ class BotTest(unittest.IsolatedAsyncioTestCase):
         # this won't be a 403 from synapse, but a LocalProtocolError from matrix_webhook
         self.assertEqual(
             bot_req({"body": 3}, KEY, "wrong_room"),
-            {"status": 403, "ret": "Unknown room"},
+            {"status": 400, "ret": "wrong_room was not legal room ID or room alias"},
         )
         self.assertEqual(
             bot_req({"body": 3}, KEY, "wrong_room", key_as_param=True),
-            {"status": 403, "ret": "Unknown room"},
+            {"status": 400, "ret": "wrong_room was not legal room ID or room alias"},
         )
 
     async def test_message(self):