diff --git a/backend/app/main.py b/backend/app/main.py
index 9e39f45d..80e22538 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -141,7 +141,7 @@ async def lifespan(_app: FastAPI) -> AsyncIterator[None]:
     finally:
         if arq_pool is not None:
             try:
-                await arq_pool.close()
+                await arq_pool.aclose()
             except Exception as exc:  # noqa: BLE001 — shutdown swallow
                 logger.warning("arq pool close raised during shutdown", error=str(exc))
         # Cancel the capability check if it's still running on shutdown
diff --git a/backend/tests/unit/test_main_lifespan.py b/backend/tests/unit/test_main_lifespan.py
index c0b26830..18344f82 100644
--- a/backend/tests/unit/test_main_lifespan.py
+++ b/backend/tests/unit/test_main_lifespan.py
@@ -83,6 +83,7 @@ def _patched_externals(monkeypatch: pytest.MonkeyPatch) -> dict[str, Any]:
     import arq.connections
 
     fake_pool = MagicMock()
+    fake_pool.aclose = AsyncMock(return_value=None)
     fake_pool.close = AsyncMock(return_value=None)
     monkeypatch.setattr(
         arq.connections,
@@ -167,6 +168,26 @@ async def _fake_warmup(db_factory: Any, redis_client: Any) -> None:
         # Warmup is gated off — coroutine NEVER called.
         assert len(warmup_invocations) == 0, warmup_invocations
 
+    async def test_lifespan_closes_arq_pool_with_aclose(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+        _patched_externals: dict[str, Any],
+    ) -> None:
+        """Regression guard: Arq pool shutdown uses non-deprecated aclose()."""
+        monkeypatch.setenv("RELYLOOP_DISABLE_STARTUP_WARMUP", "1")
+
+        async def _fake_cap_noop(**_kwargs: Any) -> None:
+            return None
+
+        monkeypatch.setattr(app_main, "run_capability_check_background", _fake_cap_noop)
+
+        app = FastAPI()
+        async with app_main.lifespan(app):
+            await asyncio.sleep(0)
+
+        _patched_externals["pool"].aclose.assert_awaited_once()
+        _patched_externals["pool"].close.assert_not_called()
+
 
 class TestLifespanShutdownCancels:
     async def test_shutdown_cancels_warmup_task_if_running(
diff --git a/backend/tests/unit/test_workers.py b/backend/tests/unit/test_workers.py
index e999290d..ad6e6ca8 100644
--- a/backend/tests/unit/test_workers.py
+++ b/backend/tests/unit/test_workers.py
@@ -14,6 +14,7 @@
 
 import os
 from pathlib import Path
+from unittest.mock import AsyncMock, MagicMock
 
 import pytest
 
@@ -111,6 +112,27 @@ def test_worker_settings_has_on_startup_hook(_settings_env: None) -> None:
     assert callable(WorkerSettings.on_startup)
 
 
+async def test_on_shutdown_closes_arq_pool_with_aclose(_settings_env: None) -> None:
+    """on_shutdown awaits ArqRedis.aclose() and avoids deprecated close()."""
+    from backend.workers.all import on_shutdown
+
+    fake_pool = MagicMock()
+    fake_pool.aclose = AsyncMock(return_value=None)
+    fake_pool.close = AsyncMock(return_value=None)
+
+    await on_shutdown({"arq_pool": fake_pool})
+
+    fake_pool.aclose.assert_awaited_once()
+    fake_pool.close.assert_not_called()
+
+
+async def test_on_shutdown_without_pool_is_noop(_settings_env: None) -> None:
+    """A missing Arq pool should not raise during worker shutdown."""
+    from backend.workers.all import on_shutdown
+
+    await on_shutdown({})
+
+
 def test_worker_settings_redis_host_parsed(_settings_env: None) -> None:
     """RedisSettings.from_dsn should pull host=redis port=6379 db=0 from the URL."""
     # Re-import so the class-level redis_settings is rebuilt with our env
diff --git a/backend/workers/all.py b/backend/workers/all.py
index e2fe60b4..b94d3823 100644
--- a/backend/workers/all.py
+++ b/backend/workers/all.py
@@ -222,7 +222,7 @@ async def on_shutdown(ctx: dict[str, Any]) -> None:
 
     arq_pool: ArqRedis | None = ctx.get("arq_pool")
     if arq_pool is not None:
-        await arq_pool.close()
+        await arq_pool.aclose()
 
 
 class WorkerSettings: