diff -r 23beb7f8561a Lib/ipaddress.py
--- a/Lib/ipaddress.py	Fri Jun 29 15:12:54 2012 +0300
+++ b/Lib/ipaddress.py	Fri Jun 29 10:49:58 2012 -0700
@@ -1249,7 +1249,8 @@
             return
 
         # Constructing from a packed address
-        if isinstance(address, bytes) and len(address) == 4:
+        if (not isinstance(address, str) and
+            isinstance(address, bytes) and len(address) == 4):
             self._ip = struct.unpack('!I', address)[0]
             return
 
@@ -1860,7 +1861,8 @@
             return
 
         # Constructing from a packed address
-        if isinstance(address, bytes) and len(address) == 16:
+        if (not isinstance(address, str) and
+            isinstance(address, bytes) and len(address) == 16):
             tmp = struct.unpack('!QQ', address)
             self._ip = (tmp[0] << 64) | tmp[1]
             return
diff -r 23beb7f8561a Lib/test/test_ipaddress.py
--- a/Lib/test/test_ipaddress.py	Fri Jun 29 15:12:54 2012 +0300
+++ b/Lib/test/test_ipaddress.py	Fri Jun 29 10:49:58 2012 -0700
@@ -106,6 +106,8 @@
         AssertInvalidIP(":1:2:3:4:5:6:7")
         AssertInvalidIP("1:2:3:4:5:6:7:")
         AssertInvalidIP(":1:2:3:4:5:6:")
+        AssertInvalidIP("1000")
+        AssertInvalidIP("1000000000000000")
 
         self.assertRaises(ipaddress.AddressValueError,
                           ipaddress.IPv4Interface, '')