diff --git a/datasette/app.py b/datasette/app.py
index 860f456322..8db650e975 100644
--- a/datasette/app.py
+++ b/datasette/app.py
@@ -44,6 +44,7 @@
 from .database import Database, QueryInterrupted
 
 from .utils import (
+    PrefixedUrlString,
     async_call_with_supported_arguments,
     await_me_maybe,
     call_with_supported_arguments,
@@ -1242,9 +1243,12 @@ class NotFoundExplicit(NotFound):
 
 class DatasetteClient:
     def __init__(self, ds):
+        self.ds = ds
         self.app = ds.app()
 
     def _fix(self, path):
+        if not isinstance(path, PrefixedUrlString):
+            path = self.ds.urls.path(path)
         if path.startswith("/"):
             path = "http://localhost{}".format(path)
         return path
diff --git a/datasette/utils/asgi.py b/datasette/utils/asgi.py
index f438f8292d..e4c8ce5ca2 100644
--- a/datasette/utils/asgi.py
+++ b/datasette/utils/asgi.py
@@ -387,9 +387,9 @@ def text(cls, body, status=200, headers=None):
         )
 
     @classmethod
-    def json(cls, body, status=200, headers=None):
+    def json(cls, body, status=200, headers=None, default=None):
         return cls(
-            json.dumps(body),
+            json.dumps(body, default=default),
             status=status,
             headers=headers,
             content_type="application/json; charset=utf-8",
diff --git a/docs/internals.rst b/docs/internals.rst
index 8594e36a0c..d3d0be8e6e 100644
--- a/docs/internals.rst
+++ b/docs/internals.rst
@@ -387,6 +387,18 @@ It offers the following methods:
 ``await datasette.client.request(method, path, **kwargs)`` - returns HTTPX Response
     Execute an internal request with the given HTTP method against that path.
 
+These methods can be used with :ref:`internals_datasette_urls` - for example:
+
+.. code-block:: python
+
+    table_json = (
+        await datasette.client.get(
+            datasette.urls.table("fixtures", "facetable", format="json")
+        )
+    ).json()
+
+``datasette.client`` methods automatically take the current :ref:`config_base_url` setting into account, whether or not you use the ``datasette.urls`` family of methods to construct the path.
+
 For documentation on available ``**kwargs`` options and the shape of the HTTPX Response object refer to the `HTTPX Async documentation <https://www.python-httpx.org/async/>`__.
 
 .. _internals_datasette_urls:
diff --git a/tests/plugins/my_plugin.py b/tests/plugins/my_plugin.py
index b487cdf0fb..767c363d63 100644
--- a/tests/plugins/my_plugin.py
+++ b/tests/plugins/my_plugin.py
@@ -257,6 +257,9 @@ def login_as_root(datasette, request):
             )
         )
 
+    def asgi_scope(scope):
+        return Response.json(scope, default=repr)
+
     return [
         (r"/one/$", one),
         (r"/two/(?P<name>.*)$", two),
@@ -267,6 +270,7 @@ def login_as_root(datasette, request):
         (r"/not-async/$", not_async),
         (r"/add-message/$", add_message),
         (r"/render-message/$", render_message),
+        (r"/asgi-scope$", asgi_scope),
     ]
 
 
diff --git a/tests/test_internals_datasette_client.py b/tests/test_internals_datasette_client.py
index d73fbb06cc..0b1c5f0e61 100644
--- a/tests/test_internals_datasette_client.py
+++ b/tests/test_internals_datasette_client.py
@@ -31,14 +31,37 @@ async def test_client_methods(datasette, method, path, expected_status):
 
 
 @pytest.mark.asyncio
-async def test_client_post(datasette):
-    response = await datasette.client.post(
-        "/-/messages",
-        data={
-            "message": "A message",
-        },
-        allow_redirects=False,
-    )
-    assert isinstance(response, httpx.Response)
-    assert response.status_code == 302
-    assert "ds_messages" in response.cookies
+@pytest.mark.parametrize("prefix", [None, "/prefix/"])
+async def test_client_post(datasette, prefix):
+    original_base_url = datasette._config["base_url"]
+    try:
+        if prefix is not None:
+            datasette._config["base_url"] = prefix
+        response = await datasette.client.post(
+            "/-/messages",
+            data={
+                "message": "A message",
+            },
+            allow_redirects=False,
+        )
+        assert isinstance(response, httpx.Response)
+        assert response.status_code == 302
+        assert "ds_messages" in response.cookies
+    finally:
+        datasette._config["base_url"] = original_base_url
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "prefix,expected_path", [(None, "/asgi-scope"), ("/prefix/", "/prefix/asgi-scope")]
+)
+async def test_client_path(datasette, prefix, expected_path):
+    original_base_url = datasette._config["base_url"]
+    try:
+        if prefix is not None:
+            datasette._config["base_url"] = prefix
+        response = await datasette.client.get("/asgi-scope")
+        path = response.json()["path"]
+        assert path == expected_path
+    finally:
+        datasette._config["base_url"] = original_base_url