diff --git a/newsfragments/4044.minor b/newsfragments/4044.minor
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/allmydata/client.py b/src/allmydata/client.py
index fefd29657..13909d5ca 100644
--- a/src/allmydata/client.py
+++ b/src/allmydata/client.py
@@ -1030,14 +1030,14 @@ class _Client(node.Node, pollmixin.PollMixin):
     def init_web(self, webport):
         self.log("init_web(webport=%s)", args=(webport,))
 
-        from allmydata.webish import WebishServer, anonymous_tempfile
+        from allmydata.webish import WebishServer, anonymous_tempfile_factory
         nodeurl_path = self.config.get_config_path("node.url")
         staticdir_config = self.config.get_config("node", "web.static", "public_html")
         staticdir = self.config.get_config_path(staticdir_config)
         ws = WebishServer(
             self,
             webport,
-            anonymous_tempfile(self._get_tempdir()),
+            anonymous_tempfile_factory(self._get_tempdir()),
             nodeurl_path,
             staticdir,
         )
diff --git a/src/allmydata/test/web/test_web.py b/src/allmydata/test/web/test_web.py
index bd7ca3f7f..42be0f50d 100644
--- a/src/allmydata/test/web/test_web.py
+++ b/src/allmydata/test/web/test_web.py
@@ -341,7 +341,7 @@ class WebMixin(TimezoneMixin):
         self.ws = webish.WebishServer(
             self.s,
             "0",
-            webish.anonymous_tempfile(tempdir.path),
+            webish.anonymous_tempfile_factory(tempdir.path),
             staticdir=self.staticdir,
             clock=self.clock,
             now_fn=lambda:self.fakeTime,
diff --git a/src/allmydata/test/web/test_webish.py b/src/allmydata/test/web/test_webish.py
index d444df436..523dfc878 100644
--- a/src/allmydata/test/web/test_webish.py
+++ b/src/allmydata/test/web/test_webish.py
@@ -6,9 +6,6 @@ import tempfile
 from uuid import (
     uuid4,
 )
-from errno import (
-    EACCES,
-)
 from io import (
     BytesIO,
 )
@@ -30,9 +27,6 @@ from testtools.matchers import (
     HasLength,
 )
 
-from twisted.python.runtime import (
-    platform,
-)
 from twisted.python.filepath import (
     FilePath,
 )
@@ -50,7 +44,7 @@ from ..common import (
 from ...webish import (
     TahoeLAFSRequest,
     TahoeLAFSSite,
-    anonymous_tempfile,
+    anonymous_tempfile_factory,
 )
 
 
@@ -179,7 +173,7 @@ class TahoeLAFSSiteTests(SyncTestCase):
         FilePath(tempdir).makedirs()
 
         site = TahoeLAFSSite(
-            anonymous_tempfile(tempdir),
+            anonymous_tempfile_factory(tempdir),
             Resource(),
             logPath=logPath,
         )
diff --git a/src/allmydata/webish.py b/src/allmydata/webish.py
index 2bae7f8a5..ec5ad64c0 100644
--- a/src/allmydata/webish.py
+++ b/src/allmydata/webish.py
@@ -4,7 +4,7 @@ General web server-related utilities.
 from __future__ import annotations
 
 from six import ensure_str
-from typing import BinaryIO, Callable, Optional
+from typing import IO, Callable, Optional
 import re, time, tempfile
 from urllib.parse import parse_qsl, urlencode
 
@@ -217,7 +217,7 @@ def censor(queryargs: bytes) -> bytes:
     return urlencode(result, safe="[]").encode("ascii")
 
 
-def anonymous_tempfile(tempdir: bytes) -> BinaryIO:
+def anonymous_tempfile_factory(tempdir: bytes) -> Callable[[], IO[bytes]]:
     """
     Create a no-argument callable for creating a new temporary file in the
     given directory.
@@ -243,14 +243,14 @@ class TahoeLAFSSite(Site, object):
     """
     requestFactory = TahoeLAFSRequest
 
-    def __init__(self, make_tempfile: Callable[[], BinaryIO], *args, **kwargs):
+    def __init__(self, make_tempfile: Callable[[], IO[bytes]], *args, **kwargs):
         Site.__init__(self, *args, logFormatter=_logFormatter, **kwargs)
         assert callable(make_tempfile)
         with make_tempfile():
             pass
         self._make_tempfile = make_tempfile
 
-    def getContentFile(self, length: Optional[int]) -> BinaryIO:
+    def getContentFile(self, length: Optional[int]) -> IO[bytes]:
         if length is None or length >= 1024 * 1024:
             return self._make_tempfile()
         return BytesIO()