diff --git a/src/allmydata/storage/http_server.py b/src/allmydata/storage/http_server.py
index 98611e833..ca8917694 100644
--- a/src/allmydata/storage/http_server.py
+++ b/src/allmydata/storage/http_server.py
@@ -10,7 +10,7 @@ from base64 import b64decode
 import binascii
 from tempfile import TemporaryFile
 
-from cryptography.x509 import Certificate
+from cryptography.x509 import Certificate as CryptoCertificate
 from zope.interface import implementer
 from klein import Klein
 from twisted.web import http
@@ -866,7 +866,7 @@ class _TLSEndpointWrapper(object):
 
 
 def build_nurl(
-    hostname: str, port: int, swissnum: str, certificate: Certificate
+    hostname: str, port: int, swissnum: str, certificate: CryptoCertificate
 ) -> DecodedURL:
     """
     Construct a HTTPS NURL, given the hostname, port, server swissnum, and x509
diff --git a/src/allmydata/test/test_istorageserver.py b/src/allmydata/test/test_istorageserver.py
index 90159f1f8..3328ea598 100644
--- a/src/allmydata/test/test_istorageserver.py
+++ b/src/allmydata/test/test_istorageserver.py
@@ -18,21 +18,14 @@ from unittest import SkipTest
 from twisted.internet.defer import inlineCallbacks, returnValue, succeed
 from twisted.internet.task import Clock
 from twisted.internet import reactor
-from twisted.internet.endpoints import serverFromString
-from twisted.python.filepath import FilePath
 from foolscap.api import Referenceable, RemoteException
 
-from allmydata.interfaces import IStorageServer  # really, IStorageClient
+# A better name for this would be IStorageClient...
+from allmydata.interfaces import IStorageServer
+
 from .common_system import SystemTestMixin
-from .common import AsyncTestCase, SameProcessStreamEndpointAssigner
-from .certs import (
-    generate_certificate,
-    generate_private_key,
-    private_key_to_file,
-    cert_to_file,
-)
+from .common import AsyncTestCase
 from allmydata.storage.server import StorageServer  # not a IStorageServer!!
-from allmydata.storage.http_server import HTTPServer, listen_tls
 from allmydata.storage.http_client import StorageClient
 from allmydata.storage_client import _HTTPStorageServer