diff --git a/README.md b/README.md
index 1261fba..b6417c2 100644
--- a/README.md
+++ b/README.md
@@ -86,7 +86,7 @@ Run the worker as usual (`arq mymodule.WorkerSettings`) and enqueue jobs with on
 |---|---|
 | `setup_di(worker_settings, container)` | Seeds the root container into arq's `ctx` and wires root + per-job lifecycle onto `on_startup`/`on_shutdown`/`on_job_start`/`on_job_end`. Accepts a `WorkerSettings` class/object or a settings `dict`; composes with existing hooks; returns the container. Raises `TypeError` if called twice on the same `worker_settings` |
 | `FromDI(dependency)` | Inert marker for `Annotated[T, FromDI(...)]` in task signatures; accepts a provider instance or a type |
-| `inject(task)` | Decorator that resolves `FromDI`-annotated parameters from the per-job `Scope.REQUEST` child. Order-insensitive; passthrough for tasks with no `FromDI`; raises `TypeError` at decoration if the task also declares `*args`/`**kwargs` |
+| `inject(task)` | Decorator that resolves `FromDI`-annotated parameters from the per-job `Scope.REQUEST` child. Order-insensitive; passthrough for tasks with no `FromDI`; raises `TypeError` at decoration if the task also declares `*args`/`**kwargs`. Raises `RuntimeError` naming `setup_di` when a job reaches it without the modern-di hooks installed |
 | `fetch_di_container(ctx)` | Returns the root container from an arq `ctx` dict |
 
 ## 📦 [PyPI](https://pypi.org/project/modern-di-arq)
diff --git a/modern_di_arq/main.py b/modern_di_arq/main.py
index 691bfc7..5f0ad0d 100644
--- a/modern_di_arq/main.py
+++ b/modern_di_arq/main.py
@@ -30,6 +30,18 @@ def _set_setting(worker_settings: typing.Any, name: str, value: typing.Any) -> N
         setattr(worker_settings, name, value)
 
 
+def _fetch_child_container(ctx: dict[str, typing.Any]) -> Container:
+    try:
+        return typing.cast(Container, ctx[_CHILD_CONTAINER_KEY])
+    except KeyError:
+        msg = (
+            "No modern-di container found for this job. "
+            "Call setup_di(worker_settings, container) so jobs pass through the modern-di hooks "
+            "before using @inject."
+        )
+        raise RuntimeError(msg) from None
+
+
 _Hook = typing.Callable[[dict[str, typing.Any]], typing.Awaitable[None]]
 
 
@@ -163,7 +175,7 @@ def inject(func: typing.Callable[..., typing.Awaitable[T]]) -> typing.Callable[.
     @functools.wraps(func)
     async def wrapper(*args: typing.Any, **kwargs: typing.Any) -> T:  # noqa: ANN401
         ctx = typing.cast("dict[str, typing.Any]", args[0])
-        child = typing.cast(Container, ctx[_CHILD_CONTAINER_KEY])
+        child = _fetch_child_container(ctx)
         # Reference-count opens so nested AND concurrent (@inject fan-out via gather)
         # share one open child and close it exactly once, when the LAST @inject body
         # exits. The check/open/increment run without an await, so asyncio cannot
diff --git a/tests/test_jobs.py b/tests/test_jobs.py
index 9754226..f1a5121 100644
--- a/tests/test_jobs.py
+++ b/tests/test_jobs.py
@@ -298,3 +298,10 @@ async def bad_task(
 
     with pytest.raises(TypeError):
         inject(bad_task)
+
+
+async def test_inject_without_setup_di_names_the_fix() -> None:
+    ctx: dict[str, typing.Any] = {}
+
+    with pytest.raises(RuntimeError, match=r"setup_di\(worker_settings, container\)"):
+        await resolves_app_and_request(ctx, 7)