diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index 20f33cbdeb67d0..12b114bbe54a25 100644
--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -1371,12 +1371,12 @@ def __init__(self, address):
         if isinstance(address, tuple):
             IPv4Address.__init__(self, address[0])
             if len(address) > 1:
-                self._prefixlen = int(address[1])
+                arg = address[1]
             else:
-                self._prefixlen = self._max_prefixlen
+                arg = self._max_prefixlen
 
             self.network = IPv4Network(address, strict=False)
-            self.netmask = self.network.netmask
+            self.netmask, self._prefixlen = self._make_netmask(arg)
             self.hostmask = self.network.hostmask
             return
 
@@ -2064,11 +2064,11 @@ def __init__(self, address):
         if isinstance(address, tuple):
             IPv6Address.__init__(self, address[0])
             if len(address) > 1:
-                self._prefixlen = int(address[1])
+                arg = address[1]
             else:
-                self._prefixlen = self._max_prefixlen
+                arg = self._max_prefixlen
             self.network = IPv6Network(address, strict=False)
-            self.netmask = self.network.netmask
+            self.netmask, self._prefixlen = self._make_netmask(arg)
             self.hostmask = self.network.hostmask
             return
 
diff --git a/Lib/test/test_ipaddress.py b/Lib/test/test_ipaddress.py
index 0e39516dc033e3..4be9f0a79a9aef 100644
--- a/Lib/test/test_ipaddress.py
+++ b/Lib/test/test_ipaddress.py
@@ -424,6 +424,10 @@ def assertBadAddress(addr, details):
         assertBadAddress("1.2.3.256", re.escape("256 (> 255)"))
 
     def test_valid_netmask(self):
+        self.assertEqual(str(self.factory(('192.0.2.0', 24))), '192.0.2.0/24')
+        self.assertEqual(str(self.factory(('192.0.2.0', '24'))), '192.0.2.0/24')
+        self.assertEqual(str(self.factory(('192.0.2.0', '255.255.255.0'))),
+                         '192.0.2.0/24')
         self.assertEqual(str(self.factory('192.0.2.0/255.255.255.0')),
                          '192.0.2.0/24')
         for i in range(0, 33):
@@ -501,6 +505,10 @@ def assertBadAddress(addr, details):
     def test_valid_netmask(self):
         # We only support CIDR for IPv6, because expanded netmasks are not
         # standard notation.
+        self.assertEqual(str(self.factory(('dead:beaf::', 32))),
+                         'dead:beaf::/32')
+        self.assertEqual(str(self.factory(('dead:beaf::', '32'))),
+                         'dead:beaf::/32')
         self.assertEqual(str(self.factory('2001:db8::/32')), '2001:db8::/32')
         for i in range(0, 129):
             # Generate and re-parse the CIDR format (trivial).