diff --git a/varlink/client.py b/varlink/client.py
index 2b60e7e..fd92b5c 100644
--- a/varlink/client.py
+++ b/varlink/client.py
@@ -9,6 +9,7 @@
 import sys
 import tempfile
 import threading
+from typing import Optional
 
 from .error import InterfaceNotFound, VarlinkEncoder, VarlinkError
 from .scanner import Interface, _Method
@@ -40,11 +41,11 @@ def __init__(self, interface, namespaced=False):
             if isinstance(member, _Method):
                 self._add_method(member)
 
-    def close(self):
+    def close(self) -> None:
         """To be implemented."""
         raise NotImplementedError
 
-    def _send_message(self, out):
+    def _send_message(self, out) -> None:
         """To be implemented.
 
         This should send a varlink message to the varlink service adding a trailing zero byte.
@@ -205,7 +206,7 @@ def __enter__(self):
     def __exit__(self, _type, _value, _traceback):
         self.close()
 
-    def close(self):
+    def close(self) -> None:
         try:
             if hasattr(self._connection, "shutdown"):
                 self._connection.shutdown(socket.SHUT_RDWR)
@@ -214,7 +215,7 @@ def close(self):
 
         self._connection.close()
 
-    def _send_message(self, out):
+    def _send_message(self, out) -> None:
         if self._send_bytes:
             self._connection.send_bytes(out + b"\0")
         elif self._sendall:
@@ -443,7 +444,7 @@ def new_bridge_socket():
             self._child_pid = p.pid
             return sp[0]
 
-        def new_bridge_socket_compat():
+        def new_bridge_socket_compat() -> socket.socket:
             sp = socket.socketpair()
             p = subprocess.Popen(
                 " ".join(argv), shell=True, stdin=subprocess.PIPE, stdout=subprocess.PIPE, close_fds=True
@@ -546,7 +547,7 @@ def _with_resolved_interface(self, interface, resolver_address=None):
 
         return self
 
-    def cleanup(self):
+    def cleanup(self) -> None:
         if hasattr(self, "_tmpdir") and self._tmpdir is not None:
             try:
                 shutil.rmtree(self._tmpdir)
@@ -563,7 +564,9 @@ def cleanup(self):
             except Exception:  # TODO: maybe just ChildProcessError?
                 pass
 
-    def open(self, interface_name, namespaced=False, connection=None):
+    def open(
+        self, interface_name: str, namespaced: bool = False, connection: Optional[socket.socket] = None
+    ) -> SimpleClientInterfaceHandler:
         """Open a new connection and get a client interface handle with the varlink methods installed.
 
         :param interface_name: an interface name, which the service this client object is
@@ -586,11 +589,12 @@ def open(self, interface_name, namespaced=False, connection=None):
 
         return self.handler(self._interfaces[interface_name], connection, namespaced=namespaced)
 
-    def open_connection(self):
+    def open_connection(self) -> socket.socket:
         """Open a new connection and return the socket.
         :exception OSError: anything socket.connect() throws
 
         """
+        assert self._socket_fn, "socket_fn not initialised"
         return self._socket_fn()
 
     def get_interfaces(self, socket_connection=None):
@@ -628,7 +632,7 @@ def get_interface(self, interface_name, socket_connection=None):
 
         return interface
 
-    def add_interface(self, interface):
+    def add_interface(self, interface: Interface) -> None:
         """Manually add or overwrite an interface definition from an Interface object.
 
         :param interface: an Interface() object
diff --git a/varlink/mock.py b/varlink/mock.py
index 1a452c7..c86a9d6 100644
--- a/varlink/mock.py
+++ b/varlink/mock.py
@@ -16,7 +16,7 @@ def cast_type(typeof):
     return cast.get(typeof, typeof)
 
 
-def get_ignored():
+def get_ignored() -> list[str]:
     ignore = dir(MockedService)
     return ignore
 
@@ -248,7 +248,7 @@ def __init__(
         product="mock",
         version=1,
         url="http://localhost",
-    ):
+    ) -> None:
         if not name:
             module = service.__module__
             try:
@@ -258,7 +258,7 @@ def __init__(
         else:
             self.name = name
         self.identifier = str(uuid.uuid4())
-        self.interface_description = None
+        self.interface_description: list[str] = []
         self.service = service
         self.types = types
         self.address = address
@@ -278,7 +278,7 @@ def __init__(
         }
         self.generate_interface()
 
-    def generate_interface(self):
+    def generate_interface(self) -> None:
         ignore = get_ignored()
         self.interface_description = [f"interface {self.name}"]
         if self.types:
@@ -288,25 +288,25 @@ def generate_interface(self):
         for attr in attributs["callables"]:
             self.interface_description.append(generate_callable_interface(self.service, attr))
 
-    def get_interface_file_path(self):
+    def get_interface_file_path(self) -> str:
         return f"/tmp/{self.name}"
 
-    def generate_interface_file(self):
+    def generate_interface_file(self) -> None:
         tfp = open(self.get_interface_file_path(), "w+")
         tfp.write("\n".join(self.interface_description))
         tfp.close()
 
-    def delete_interface_files(self):
+    def delete_interface_files(self) -> None:
         os.remove(self.get_interface_file_path())
         os.remove(self.mocked_service_file)
 
-    def service_start(self):
+    def service_start(self) -> None:
         self.service_pid = subprocess.Popen(
             [sys.executable, self.mocked_service_file], env={"PYTHONPATH": ":".join(sys.path)}
         )
         time.sleep(2)
 
-    def service_stop(self):
+    def service_stop(self) -> None:
         self.service_pid.kill()
         self.service_pid.communicate()
 
diff --git a/varlink/server.py b/varlink/server.py
index 8031cd5..f8a128c 100644
--- a/varlink/server.py
+++ b/varlink/server.py
@@ -12,7 +12,7 @@
     from socketserver import ForkingMixIn
 
 from types import GeneratorType
-from typing import Optional
+from typing import Optional, Union
 
 
 class Service:
@@ -91,7 +91,7 @@ def GetInfo(self):
             "interfaces": list(self.interfaces.keys()),
         }
 
-    def GetInterfaceDescription(self, interface):
+    def GetInterfaceDescription(self, interface: str) -> dict[str, str]:
         """The standardized org.varlink.service.GetInterfaceDescription() varlink method."""
         try:
             i = self.interfaces[interface]
@@ -282,7 +282,7 @@ def decorator(interface_class):
         return decorator
 
 
-def get_listen_fd():
+def get_listen_fd() -> Union[int, None]:
     if "LISTEN_FDS" not in os.environ:
         return None
     if "LISTEN_PID" not in os.environ:
@@ -319,6 +319,8 @@ def get_listen_fd():
             except OSError:
                 return None
 
+    return None
+
 
 class RequestHandler(StreamRequestHandler):
     """Varlink request handler
@@ -500,7 +502,7 @@ def server_close(self):
                 pass
         self.socket.close()
 
-    def fileno(self):
+    def fileno(self) -> int:
         """Return socket file number.
 
         Interface required by selector.
diff --git a/varlink/tests/test_basic_network.py b/varlink/tests/test_basic_network.py
index fcabe3b..611c80e 100755
--- a/varlink/tests/test_basic_network.py
+++ b/varlink/tests/test_basic_network.py
@@ -43,18 +43,39 @@ def do_run(self, address):
             server.shutdown()
             server.server_close()
 
-    def test_tcp(self):
+    def test_tcp(self) -> None:
         self.do_run("tcp:127.0.0.1:23450")
 
-    def test_anon_unix(self):
+    def test_anon_unix(self) -> None:
         if platform.startswith("linux"):
             self.do_run(f"unix:@org.varlink.service_anon_test{os.getpid()}{threading.current_thread().name}")
 
-    def test_unix(self):
+    def test_unix(self) -> None:
         if hasattr(socket, "AF_UNIX"):
             self.do_run(f"unix:org.varlink.service_anon_test_{os.getpid()}{threading.current_thread().name}")
 
-    def test_wrong_url(self):
+    def test_wrong_url(self) -> None:
         self.assertRaises(
             ConnectionError, self.do_run, f"uenix:org.varlink.service_wrong_url_test_{os.getpid()}"
         )
+
+    def test_reuse_open(self) -> None:
+        address = "tcp:127.0.0.1:23450"
+        server = varlink.ThreadingServer(address, ServiceRequestHandler)
+        server_thread = threading.Thread(target=server.serve_forever)
+        server_thread.daemon = True
+        server_thread.start()
+
+        try:
+            with varlink.Client(address) as client:
+                connection = client.open_connection()
+                re_use = client.open("org.varlink.service", False, connection)
+
+                info = re_use.GetInfo()
+                self.assertEqual(len(info["interfaces"]), 1)
+                self.assertEqual(info["interfaces"][0], "org.varlink.service")
+                self.assertEqual(info, service.GetInfo())
+                connection.close()
+        finally:
+            server.shutdown()
+            server.server_close()
diff --git a/varlink/tests/test_orgexamplemore.py b/varlink/tests/test_orgexamplemore.py
index 46ae92b..561e231 100755
--- a/varlink/tests/test_orgexamplemore.py
+++ b/varlink/tests/test_orgexamplemore.py
@@ -88,7 +88,7 @@ def __init__(self, reason):
 
 @service.interface("org.example.more")
 class Example:
-    sleep_duration = 1
+    sleep_duration = 1.0
 
     def TestMore(self, n, _more=True, _server=None):
         try:
@@ -214,7 +214,7 @@ def epilog():
 
 
 class TestService(unittest.TestCase):
-    def test_service(self):
+    def test_service(self) -> None:
         address = "tcp:127.0.0.1:23451"
         Example.sleep_duration = 0.1