diff --git a/README.md b/README.md
index c91f9cc..83052fc 100644
--- a/README.md
+++ b/README.md
@@ -94,7 +94,7 @@ def my_command(ctx: typer.Context) -> None:
 - `setup_di(app, container)` — register the container with a Typer app
 - `inject` — decorator that resolves `FromDI`-annotated parameters before the command runs; also exposes `typer.Context` with `ctx.obj["di_container"]` for manual use. Raises `RuntimeError` naming `setup_di` when a command reaches it without `setup_di` called
 - `FromDI(provider)` — marker used in `Annotated[T, FromDI(...)]`; accepts a provider instance or a type
-- `action_scope(ctx)` — context manager yielding a fresh `Scope.ACTION` container (a child of the command container); open one per action
+- `action_scope(ctx)` — context manager yielding a fresh `Scope.ACTION` container (a child of the command container); open one per action. Raises `RuntimeError` naming `@inject` when called from a command without it
 - `fetch_di_container(ctx)` — returns the app-scoped container from `ctx.obj`
 
 ## Used by
diff --git a/modern_di_typer/main.py b/modern_di_typer/main.py
index 25a77b5..bb2f980 100644
--- a/modern_di_typer/main.py
+++ b/modern_di_typer/main.py
@@ -43,7 +43,14 @@ def _build_command_container(ctx: typer.Context) -> typing.Iterator[Container]:
 
 @contextlib.contextmanager
 def action_scope(ctx: typer.Context) -> typing.Iterator[Container]:
-    request_container: Container = ctx.meta[_COMMAND_CONTAINER_KEY]
+    try:
+        request_container: Container = ctx.meta[_COMMAND_CONTAINER_KEY]
+    except KeyError:
+        msg = (
+            "No modern-di command container found for this command. "
+            "Decorate the command with @inject so action_scope has a per-command container to nest under."
+        )
+        raise RuntimeError(msg) from None
     with request_container.build_child_container() as action_container:
         yield action_container
 
diff --git a/tests/test_commands.py b/tests/test_commands.py
index c23dd0f..6941586 100644
--- a/tests/test_commands.py
+++ b/tests/test_commands.py
@@ -284,3 +284,15 @@ def cmd(ctx: typer.Context) -> None:
 
     with pytest.raises(RuntimeError, match=r"setup_di\(app, container\)"):
         runner.invoke(app, catch_exceptions=False)
+
+
+def test_action_scope_without_inject_raises_clear_error(app: typer.Typer) -> None:
+    runner = CliRunner()
+
+    @app.command()
+    def cmd(ctx: typer.Context) -> None:
+        with action_scope(ctx):
+            ...
+
+    with pytest.raises(RuntimeError, match="@inject"):
+        runner.invoke(app, catch_exceptions=False)