diff --git a/datasette/app.py b/datasette/app.py
index 8db650e9..1271e52f 100644
--- a/datasette/app.py
+++ b/datasette/app.py
@@ -822,6 +822,9 @@ class Datasette:
             if url in seen_urls:
                 continue
             seen_urls.add(url)
+            if url.startswith("/"):
+                # Take base_url into account:
+                url = self.urls.path(url)
             if sri:
                 output.append({"url": url, "sri": sri})
             else:
diff --git a/datasette/utils/__init__.py b/datasette/utils/__init__.py
index 21fa944c..a7d96401 100644
--- a/datasette/utils/__init__.py
+++ b/datasette/utils/__init__.py
@@ -1,8 +1,8 @@
 import asyncio
 from contextlib import contextmanager
+import click
 from collections import OrderedDict, namedtuple
 import base64
-import click
 import hashlib
 import inspect
 import itertools
@@ -1016,8 +1016,11 @@ class PrefixedUrlString(str):
     def __add__(self, other):
         return type(self)(super().__add__(other))
 
+    def __str__(self):
+        return super().__str__()
+
     def __getattribute__(self, name):
-        if name in dir(str):
+        if not name.startswith("__") and name in dir(str):
 
             def method(self, *args, **kwargs):
                 value = getattr(super(), name)(*args, **kwargs)
diff --git a/tests/fixtures.py b/tests/fixtures.py
index 5cbfc72f..d2ac661d 100644
--- a/tests/fixtures.py
+++ b/tests/fixtures.py
@@ -274,6 +274,7 @@ METADATA = {
     "source_url": "https://github.com/simonw/datasette/blob/master/tests/fixtures.py",
     "about": "About Datasette",
     "about_url": "https://github.com/simonw/datasette",
+    "extra_css_urls": ["/static/extra-css-urls.css"],
     "plugins": {
         "name-of-plugin": {"depth": "root"},
         "env-plugin": {"foo": {"$env": "FOO_ENV"}},
diff --git a/tests/test_api.py b/tests/test_api.py
index 5e9c1a0a..18e4b9e4 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -1852,6 +1852,7 @@ def test_paginate_using_link_header(app_client, qs):
     num_pages = 0
     while path:
         response = app_client.get(path)
+        assert response.status == 200
         num_pages += 1
         link = response.headers.get("link")
         if link:
diff --git a/tests/test_cli_serve_get.py b/tests/test_cli_serve_get.py
index 8f1665a9..39236dd8 100644
--- a/tests/test_cli_serve_get.py
+++ b/tests/test_cli_serve_get.py
@@ -61,6 +61,7 @@ def test_serve_with_get_exit_code_for_error(tmp_path_factory):
             "--get",
             "/this-is-404",
         ],
+        catch_exceptions=False,
     )
     assert result.exit_code == 1
     assert "404" in result.output
diff --git a/tests/test_html.py b/tests/test_html.py
index 79b6138d..006c223d 100644
--- a/tests/test_html.py
+++ b/tests/test_html.py
@@ -1466,6 +1466,11 @@ def test_base_url_config(app_client_base_url_prefix, path):
             }
 
 
+def test_base_url_affects_metadata_extra_css_urls(app_client_base_url_prefix):
+    html = app_client_base_url_prefix.get("/").text
+    assert '<link rel="stylesheet" href="/prefix/static/extra-css-urls.css">' in html
+
+
 @pytest.mark.parametrize(
     "path,expected",
     [