diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index 15507d61dec8f9..169bf9ba7432fe 100644
--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -1519,7 +1519,13 @@ def __init__(self, address, strict=True):
         # Constructing from a tuple (addr, [mask])
         elif isinstance(address, tuple):
             addr = address[0]
-            mask = address[1] if len(address) > 1 else self._max_prefixlen
+            if len(address) > 1:
+                if isinstance(address[1], int) and address[1] > 32:
+                    raise NetmaskValueError(f"The netmask is not valid {address[1]}")
+                mask = address[1]
+            else:
+                mask = self._max_prefixlen
+            #mask = address[1] if len(address) > 1 else self._max_prefixlen
         # Assume input argument to be string or any object representation
         # which converts into a formatted IP prefix string.
         else:
diff --git a/Lib/test/test_ipaddress.py b/Lib/test/test_ipaddress.py
index 0e0753f34c4905..373eb5e828aedf 100644
--- a/Lib/test/test_ipaddress.py
+++ b/Lib/test/test_ipaddress.py
@@ -839,6 +839,8 @@ def testIPv4Tuple(self):
         # strict=True and host bits set
         with self.assertRaises(ValueError):
             ipaddress.IPv4Network(('192.0.2.1', 24))
+        with self.assertRaises(ValueError):
+            ipaddress.IPv4Network(('192.0.2.1', 33))
         with self.assertRaises(ValueError):
             ipaddress.IPv4Network((ip, 24))
         with self.assertRaises(ValueError):
diff --git a/Misc/NEWS.d/next/Library/2019-02-13-21-43-31.bpo-35989.8L9aBw.rst b/Misc/NEWS.d/next/Library/2019-02-13-21-43-31.bpo-35989.8L9aBw.rst
new file mode 100644
index 00000000000000..810a4828e12e08
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-02-13-21-43-31.bpo-35989.8L9aBw.rst
@@ -0,0 +1,2 @@
+IPv4Network raises a ``NetmaskValueError`` exception if the netmask is not
+between 0 and 32. Contributed by Stéphane Wirtel.