diff --git a/logistics_chat/db.py b/logistics_chat/db.py
index 1937715..fbe7d08 100644
--- a/logistics_chat/db.py
+++ b/logistics_chat/db.py
@@ -37,6 +37,8 @@ def init_db():
     Path(get_setting('DATABASE')).parent.mkdir(parents=True, exist_ok=True)
     conn = connect()
     cur = conn.cursor()
+    # Serialize schema inspection and migration when multiple workers start together.
+    cur.execute('BEGIN IMMEDIATE')
     cur.execute('''
     CREATE TABLE IF NOT EXISTS chat_history (
         id INTEGER PRIMARY KEY AUTOINCREMENT,
diff --git a/tests/test_storage.py b/tests/test_storage.py
index 230616a..7483502 100644
--- a/tests/test_storage.py
+++ b/tests/test_storage.py
@@ -6,6 +6,8 @@ from pathlib import Path
 import tempfile
 import time
 import unittest
+from concurrent.futures import ThreadPoolExecutor
+from threading import Barrier
 
 from flask import Flask
 from werkzeug.datastructures import FileStorage
@@ -29,6 +31,27 @@ class StorageTests(unittest.TestCase):
         self.addCleanup(self.context.pop)
         db.init_db()
 
+    def test_concurrent_startup_migrates_legacy_history_once_without_claiming_it(self):
+        connection = db.connect()
+        connection.executescript('DROP TABLE chat_history; CREATE TABLE chat_history '
+            '(id INTEGER PRIMARY KEY, title TEXT NOT NULL, ctime TEXT NOT NULL);'
+            "INSERT INTO chat_history VALUES(1,'旧记录','now');")
+        connection.close()
+        gate = Barrier(4)
+
+        def initialize():
+            with self.app.app_context():
+                gate.wait(timeout=5)
+                db.init_db()
+
+        with ThreadPoolExecutor(max_workers=4) as workers:
+            for result in workers.map(lambda _: initialize(), range(4)):
+                self.assertIsNone(result)
+        connection = db.connect()
+        self.assertEqual(connection.execute('SELECT title, visitor_id FROM chat_history').fetchall(), [('旧记录', None)])
+        self.assertEqual(connection.execute('SELECT COUNT(*) FROM messages WHERE conv_id=1').fetchone()[0], 1)
+        connection.close()
+
     def test_old_schema_is_migrated_and_legacy_title_backfilled(self):
         connection = db.connect()
         connection.executescript('DROP TABLE chat_history; CREATE TABLE chat_history '