diff --git a/acme/acme/_internal/tests/crypto_util_test.py b/acme/acme/_internal/tests/crypto_util_test.py
index ae1821794..2aca0f3fb 100644
--- a/acme/acme/_internal/tests/crypto_util_test.py
+++ b/acme/acme/_internal/tests/crypto_util_test.py
@@ -44,6 +44,7 @@ class SSLSocketAndProbeSNITest(unittest.TestCase):
         if self.server_thread.is_alive():
             # The thread may have already terminated.
             self.server_thread.join()  # pragma: no cover
+        self.server.server_close()
 
     def _probe(self, name):
         from acme.crypto_util import probe_sni
diff --git a/acme/acme/_internal/tests/standalone_test.py b/acme/acme/_internal/tests/standalone_test.py
index 130d8dc7d..85b05dbc8 100644
--- a/acme/acme/_internal/tests/standalone_test.py
+++ b/acme/acme/_internal/tests/standalone_test.py
@@ -55,6 +55,7 @@ class HTTP01ServerTest(unittest.TestCase):
     def tearDown(self):
         self.server.shutdown()
         self.thread.join()
+        self.server.server_close()
 
     def test_index(self):
         response = requests.get(
@@ -133,6 +134,7 @@ class TLSALPN01ServerTest(unittest.TestCase):
     def tearDown(self):
         self.server.shutdown()  # pylint: disable=no-member
         self.thread.join()
+        self.server.server_close()
 
     # TODO: This is not implemented yet, see comments in standalone.py
     # def test_certs(self):
@@ -214,6 +216,8 @@ class BaseDualNetworkedServersTest(unittest.TestCase):
             if prev_port:
                 assert prev_port == port
             prev_port = port
+        for server in servers.servers:
+            server.server_close()
 
 
 class HTTP01DualNetworkedServersTest(unittest.TestCase):