diff --git a/backend/src/module/database/engine.py b/backend/src/module/database/engine.py
index 6ae8bb09..602f16f2 100644
--- a/backend/src/module/database/engine.py
+++ b/backend/src/module/database/engine.py
@@ -1,14 +1,12 @@
 from sqlalchemy import event
 from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
 from sqlalchemy.orm import sessionmaker
-from sqlmodel import create_engine
 
 from module.conf import DATA_PATH
 
-# Sync engine (used by Database, which owns a Session)
-engine = create_engine(DATA_PATH)
-
-# Async engine (for passkey operations)
+# The whole application runs on the async engine now. DATA_PATH (the sync
+# sqlite URL) is kept only to derive the async URL and for the migration tests,
+# which build their own throwaway sync engine.
 ASYNC_DATA_PATH = DATA_PATH.replace("sqlite:///", "sqlite+aiosqlite:///")
 async_engine = create_async_engine(ASYNC_DATA_PATH)
 async_session_factory = sessionmaker(
@@ -16,13 +14,6 @@ async_session_factory = sessionmaker(
 )
 
 
-@event.listens_for(engine, "connect")
-def _set_sqlite_fk_sync(dbapi_conn, connection_record):
-    cursor = dbapi_conn.cursor()
-    cursor.execute("PRAGMA foreign_keys=ON")
-    cursor.close()
-
-
 def _set_sqlite_pragmas_async(dbapi_conn, connection_record):
     """Per-connection SQLite pragmas for the async engine.