diff -r d9e25fe35f46 Lib/socketserver.py
--- a/Lib/socketserver.py	Tue Aug 02 22:30:24 2016 +0200
+++ b/Lib/socketserver.py	Tue Aug 02 16:06:43 2016 -0700
@@ -433,6 +433,13 @@
     def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
         """Constructor.  May be extended, do not override."""
         BaseServer.__init__(self, server_address, RequestHandlerClass)
+        try:
+            gai_results = socket.getaddrinfo(*server_address,
+                                             type=self.socket_type)
+            # This allows AF_INET6 to automatically used if the supported.
+            self.address_family = gai_results[0][0]
+        except socket.gaierror:
+            pass  # Use the default.
         self.socket = socket.socket(self.address_family,
                                     self.socket_type)
         if bind_and_activate: