diff --git a/src/calibre/gui2/actions/device.py b/src/calibre/gui2/actions/device.py
index 1fc26ca647..656fc5be79 100644
--- a/src/calibre/gui2/actions/device.py
+++ b/src/calibre/gui2/actions/device.py
@@ -16,15 +16,9 @@ from calibre.utils.smtp import config as email_config
 
 
 def local_url_for_content_server():
-    def is_ipv6_addr(addr):
-        import socket
-        try:
-            socket.inet_pton(socket.AF_INET6, addr)
-            return True
-        except OSError:
-            return False
-
     from calibre.srv.opts import server_config
+    from calibre.utils.network import is_ipv6_addr
+
     opts = server_config()
     interface = opts.listen_on or '0.0.0.0'
 
diff --git a/src/calibre/gui2/preferences/server.py b/src/calibre/gui2/preferences/server.py
index 98a3b783d3..65aa700d55 100644
--- a/src/calibre/gui2/preferences/server.py
+++ b/src/calibre/gui2/preferences/server.py
@@ -1299,13 +1299,7 @@ class ConfigWidget(ConfigWidgetBase):
         self.stopping_msg.accept()
 
     def test_server(self):
-        def is_ipv6_addr(addr):
-            import socket
-            try:
-                socket.inet_pton(socket.AF_INET6, addr)
-                return True
-            except OSError:
-                return False
+        from calibre.utils.network import is_ipv6_addr
 
         prefix = self.advanced_tab.get('url_prefix') or ''
         protocol = 'https' if self.advanced_tab.has_ssl else 'http'
diff --git a/src/calibre/srv/loop.py b/src/calibre/srv/loop.py
index 4fc4f68738..beb02b8bdf 100644
--- a/src/calibre/srv/loop.py
+++ b/src/calibre/srv/loop.py
@@ -508,13 +508,7 @@ class ServerLoop:
             self.setup_socket()
 
     def serve(self):
-        def is_ipv6_addr(addr):
-            import socket
-            try:
-                socket.inet_pton(socket.AF_INET6, addr)
-                return True
-            except OSError:
-                return False
+        from calibre.utils.network import is_ipv6_addr
 
         self.connection_map = {}
         if not self.socket_was_preactivated:
diff --git a/src/calibre/utils/network.py b/src/calibre/utils/network.py
index 410206df81..ca469f9c89 100644
--- a/src/calibre/utils/network.py
+++ b/src/calibre/utils/network.py
@@ -108,3 +108,11 @@ def internet_connected():
         DummyNetworkStatus()
 
     return internet_connected.checker()
+
+def is_ipv6_addr(addr):
+    import socket
+    try:
+        socket.inet_pton(socket.AF_INET6, addr)
+        return True
+    except OSError:
+        return False