diff --git a/fastapi/routing.py b/fastapi/routing.py
index 5354cfa3a5..eaaeee7481 100644
--- a/fastapi/routing.py
+++ b/fastapi/routing.py
@@ -996,18 +996,12 @@ class APIRouter(routing.Router):
 
     def mount(self, path: str, app: ASGIApp, name: str | None = None) -> None:
         """
-        Mount a `StaticFiles` instance at the given path.
-
-        Raises `FastAPIError` if `app` is not an instance of `StaticFiles`,
-        since mounting arbitrary ASGI sub-applications under an `APIRouter`
-        is not supported. Sub-applications should be mounted directly on
-        the root `FastAPI` instance instead.
+        Mount a StaticFiles instance.
+        Will raise a FastAPIError exception if app is not an instance of StaticFiles.
         """
         if not isinstance(app, StaticFiles):
             raise FastAPIError(
-                "APIRouter does not support mounting ASGI applications other than "
-                "StaticFiles. Mount sub-applications directly on the root FastAPI "
-                "instance instead."
+                "APIRouter does not support mounting ASGI applications other than StaticFiles."
             )
         self._mount(path=path, app=app, name=name)
 
diff --git a/tests/test_router_mount.py b/tests/test_apirouter_mount.py
similarity index 98%
rename from tests/test_router_mount.py
rename to tests/test_apirouter_mount.py
index e0b19d1937..1a2de54822 100644
--- a/tests/test_router_mount.py
+++ b/tests/test_apirouter_mount.py
@@ -76,6 +76,6 @@ def test_mount_non_staticfiles_app_raises_error() -> None:
 
     with pytest.raises(
         FastAPIError,
-        match="APIRouter does not support mounting ASGI applications other than StaticFiles",
+        match="APIRouter does not support mounting ASGI applications other than StaticFiles.",
     ):
         router.mount("/sub", sub_app)