diff --git a/Lib/asyncio/unix_events.py b/Lib/asyncio/unix_events.py
index 2125548..1fbdd31 100644
--- a/Lib/asyncio/unix_events.py
+++ b/Lib/asyncio/unix_events.py
@@ -206,6 +206,10 @@
             raise TypeError('ssl argument must be an SSLContext or None')
 
         if path is not None:
+            if sock is not None:
+                raise ValueError(
+                    'path and sock can not be specified at the same time')
+
             sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
 
             try:
diff --git a/Lib/test/test_asyncio/test_events.py b/Lib/test/test_asyncio/test_events.py
index bafa875..1e64dd0 100644
--- a/Lib/test/test_asyncio/test_events.py
+++ b/Lib/test/test_asyncio/test_events.py
@@ -703,6 +703,17 @@
         # close server
         server.close()
 
+    @unittest.skipUnless(hasattr(socket, 'AF_UNIX'), 'No UNIX Sockets')
+    def test_create_unix_server_path_socket_error(self):
+        proto = MyProto(loop=self.loop)
+        sock = socket.socket()
+        with sock:
+            f = self.loop.create_unix_server(lambda: proto, '/test', sock=sock)
+            with self.assertRaisesRegex(ValueError,
+                                        'path and sock can not be specified '
+                                        'at the same time'):
+                server = self.loop.run_until_complete(f)
+
     def _create_ssl_context(self, certfile, keyfile=None):
         sslcontext = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
         sslcontext.options |= ssl.OP_NO_SSLv2
diff --git a/Misc/NEWS b/Misc/NEWS
index fd5e71b..ec4ea5c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -27,6 +27,9 @@
 Library
 -------
 
+- Issue #21155: asyncio.EventLoop.create_unix_server() now raises a ValueError
+  if path and sock are specified at the same time.
+
 - Issue #21149: Improved thread-safety in logging cleanup during interpreter
   shutdown. Thanks to Devin Jeanpierre for the patch.