diff --git a/README.md b/README.md
index a39b779..62d25d1 100644
--- a/README.md
+++ b/README.md
@@ -89,6 +89,8 @@ app.router.add_view("/users", Users)
 
 An HTTP request opens a `Scope.REQUEST` child container; a WebSocket connection opens a `Scope.SESSION` one. The connection `aiohttp.web.Request` is resolvable within DI: HTTP handlers and `REQUEST`-scoped factories inject it by type via `aiohttp_request_provider`, while WebSocket handlers read it via `FromDI(aiohttp_websocket_provider)`. For per-message work inside a WebSocket handler, open a nested `Scope.REQUEST` child of the session container fetched with `fetch_request_container`.
 
+Sub-apps added with `app.add_subapp` work with or without their own `setup_di`. When both the parent and the sub-app call `setup_di`, a sub-app route resolves from a child of the sub-app's root container, and the parent's middleware still opens and closes its own child container around it. When only the parent calls `setup_di`, a sub-app route resolves from a child of the parent's root container.
+
 ## API
 
 | Symbol | Description |
diff --git a/modern_di_aiohttp/main.py b/modern_di_aiohttp/main.py
index 63863d9..8a06592 100644
--- a/modern_di_aiohttp/main.py
+++ b/modern_di_aiohttp/main.py
@@ -70,13 +70,17 @@ async def _di_middleware(
     async with fetch_di_container(request.app).build_child_container(
         scope=match.scope, context=match.context
     ) as child_container:
+        outer_container = request.get(_CONTAINER_REQUEST_KEY)
         request[_CONTAINER_REQUEST_KEY] = child_container
         try:
             return await handler(request)
         finally:
             # The container's context holds this request, so leaving the entry behind closes a
             # cycle and the request could only be reclaimed by the GC.
-            del request[_CONTAINER_REQUEST_KEY]
+            if outer_container is None:
+                del request[_CONTAINER_REQUEST_KEY]
+            else:
+                request[_CONTAINER_REQUEST_KEY] = outer_container
 
 
 def setup_di(app: web.Application, container: Container) -> Container:
diff --git a/tests/test_subapps.py b/tests/test_subapps.py
new file mode 100644
index 0000000..eb5f10f
--- /dev/null
+++ b/tests/test_subapps.py
@@ -0,0 +1,90 @@
+import collections.abc
+import dataclasses
+import http
+import typing
+
+from aiohttp import web
+from aiohttp.test_utils import TestClient
+from modern_di import Container, Group, Scope, providers
+from modern_di.providers import CacheSettings
+
+from modern_di_aiohttp import FromDI, fetch_request_container, inject, setup_di
+
+
+AiohttpClient = collections.abc.Callable[[web.Application], collections.abc.Awaitable[TestClient]]
+
+
+@dataclasses.dataclass(kw_only=True, slots=True)
+class Label:
+    name: str
+
+
+def make_group(name: str, finalized: list[str]) -> type[Group]:
+    class AppDependencies(Group):
+        label = providers.Factory(
+            scope=Scope.REQUEST,
+            creator=lambda: Label(name=name),
+            bound_type=Label,
+            cache=CacheSettings(finalizer=lambda label: finalized.append(label.name)),
+        )
+
+    return AppDependencies
+
+
+@inject
+async def label_view(
+    request: web.Request,  # noqa: ARG001
+    label: typing.Annotated[Label, FromDI(Label)],
+) -> web.Response:
+    return web.Response(text=label.name)
+
+
+@web.middleware
+async def resolve_label_middleware(
+    request: web.Request,
+    handler: typing.Callable[[web.Request], typing.Awaitable[web.StreamResponse]],
+) -> web.StreamResponse:
+    fetch_request_container(request).resolve(Label)
+    return await handler(request)
+
+
+def build_apps(*, sub_has_di: bool, finalized: list[str]) -> web.Application:
+    sub = web.Application()
+    sub.router.add_get("/x", label_view)
+    if sub_has_di:
+        setup_di(sub, Container(groups=[make_group("sub", finalized)]))
+
+    parent = web.Application()
+    parent.router.add_get("/x", label_view)
+    setup_di(parent, Container(groups=[make_group("parent", finalized)]))
+    parent.middlewares.append(resolve_label_middleware)
+    parent.add_subapp("/sub", sub)
+    return parent
+
+
+async def test_each_app_resolves_from_its_own_container(aiohttp_client: AiohttpClient) -> None:
+    client = await aiohttp_client(build_apps(sub_has_di=True, finalized=[]))
+
+    parent_response = await client.get("/x")
+    assert parent_response.status == http.HTTPStatus.OK
+    assert await parent_response.text() == "parent"
+
+    sub_response = await client.get("/sub/x")
+    assert sub_response.status == http.HTTPStatus.OK
+    assert await sub_response.text() == "sub"
+
+
+async def test_sub_app_without_setup_di_resolves_from_parent(aiohttp_client: AiohttpClient) -> None:
+    client = await aiohttp_client(build_apps(sub_has_di=False, finalized=[]))
+
+    response = await client.get("/sub/x")
+    assert response.status == http.HTTPStatus.OK
+    assert await response.text() == "parent"
+
+
+async def test_both_child_containers_closed_after_sub_app_request(aiohttp_client: AiohttpClient) -> None:
+    finalized: list[str] = []
+    client = await aiohttp_client(build_apps(sub_has_di=True, finalized=finalized))
+
+    assert (await client.get("/sub/x")).status == http.HTTPStatus.OK
+    assert sorted(finalized) == ["parent", "sub"]