diff --git a/electrum/gui/qt/network_dialog.py b/electrum/gui/qt/network_dialog.py
index 268e01b7f..7949eab5a 100644
--- a/electrum/gui/qt/network_dialog.py
+++ b/electrum/gui/qt/network_dialog.py
@@ -33,7 +33,7 @@ import PyQt5.QtCore as QtCore
 from electrum.i18n import _
 from electrum import constants, blockchain
 from electrum.util import print_error
-from electrum.network import serialize_server, deserialize_server
+from electrum.interface import serialize_server, deserialize_server
 
 from .util import *
 
@@ -337,7 +337,7 @@ class NetworkChoiceLayout(object):
     def update(self):
         host, port, protocol, proxy_config, auto_connect = self.network.get_parameters()
         self.server_host.setText(host)
-        self.server_port.setText(port)
+        self.server_port.setText(str(port))
         self.autoconnect_cb.setChecked(auto_connect)
 
         interface = self.network.interface
diff --git a/electrum/interface.py b/electrum/interface.py
index 5cdcd4297..2b63c1978 100644
--- a/electrum/interface.py
+++ b/electrum/interface.py
@@ -30,6 +30,7 @@ import sys
 import traceback
 import asyncio
 import concurrent.futures
+from typing import Tuple, Union
 
 import aiorpcx
 from aiorpcx import ClientSession, Notification, TaskGroup
@@ -83,14 +84,28 @@ class CustomTaskGroup(TaskGroup):
         return super().spawn(*args, **kwargs)
 
 
+def deserialize_server(server_str: str) -> Tuple[str, int, str]:
+    # host might be IPv6 address, hence do rsplit:
+    host, port, protocol = str(server_str).rsplit(':', 2)
+    if protocol not in ('s', 't'):
+        raise ValueError('invalid network protocol: {}'.format(protocol))
+    port = int(port)  # Throw if cannot be converted to int
+    if not (0 < port < 2**16):
+        raise ValueError('port {} is out of valid range'.format(port))
+    return host, port, protocol
+
+
+def serialize_server(host: str, port: Union[str, int], protocol: str) -> str:
+    return str(':'.join([host, str(port), protocol]))
+
+
 class Interface(PrintError):
 
     def __init__(self, network, server, config_path, proxy):
         self.exception = None
         self.ready = asyncio.Future()
         self.server = server
-        self.host, self.port, self.protocol = self.server.split(':')
-        self.port = int(self.port)
+        self.host, self.port, self.protocol = deserialize_server(self.server)
         self.config_path = config_path
         self.cert_path = os.path.join(self.config_path, 'certs', self.host)
         self.tip_header = None
diff --git a/electrum/network.py b/electrum/network.py
index 5858ed213..ebe40f058 100644
--- a/electrum/network.py
+++ b/electrum/network.py
@@ -20,7 +20,6 @@
 # ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 # CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 # SOFTWARE.
-import concurrent.futures
 import time
 import queue
 import os
@@ -33,7 +32,6 @@ import json
 import sys
 import ipaddress
 import asyncio
-import concurrent.futures
 
 import dns
 import dns.resolver
@@ -44,7 +42,7 @@ from .util import PrintError, print_error, aiosafe, bfh
 from .bitcoin import COIN
 from . import constants
 from . import blockchain
-from .interface import Interface
+from .interface import Interface, serialize_server, deserialize_server
 from .version import PROTOCOL_VERSION
 
 NODES_RETRY_INTERVAL = 60
@@ -126,6 +124,7 @@ def deserialize_proxy(s):
     if s.lower() == 'none':
         return None
     proxy = { "mode":"socks5", "host":"localhost" }
+    # FIXME raw IPv6 address fails here
     args = s.split(':')
     n = 0
     if proxy_modes.count(args[n]) == 1:
@@ -147,19 +146,9 @@ def deserialize_proxy(s):
     return proxy
 
 
-def deserialize_server(server_str):
-    host, port, protocol = str(server_str).rsplit(':', 2)
-    if protocol not in 'st':
-        raise ValueError('invalid network protocol: {}'.format(protocol))
-    int(port)    # Throw if cannot be converted to int
-    return host, port, protocol
-
-
-def serialize_server(host, port, protocol):
-    return str(':'.join([host, port, protocol]))
-
 INSTANCE = None
 
+
 class Network(PrintError):
     """The Network class manages a set of connections to remote electrum
     servers, each connected socket is handled by an Interface() object.
@@ -794,7 +783,7 @@ class Network(PrintError):
             if self.interface:
                 server = self.interface.server
                 host, port, protocol, proxy, auto_connect = self.get_parameters()
-                host, port, protocol = server.split(':')
+                host, port, protocol = deserialize_server(server)
                 self.set_parameters(host, port, protocol, proxy, auto_connect)
 
     def get_local_height(self):