diff -r 06cf4044a11a Lib/pathlib.py
--- a/Lib/pathlib.py	Sat Aug 09 09:34:25 2014 +0300
+++ b/Lib/pathlib.py	Sat Aug 09 14:52:29 2014 +0700
@@ -50,6 +50,8 @@
         self.join = self.sep.join
 
     def parse_parts(self, parts):
+        if any(map(lambda arg: '\0' in arg, parts)):
+            raise TypeError("embedded NUL character")
         parsed = []
         sep = self.sep
         altsep = self.altsep
diff -r 06cf4044a11a Lib/test/test_pathlib.py
--- a/Lib/test/test_pathlib.py	Sat Aug 09 09:34:25 2014 +0300
+++ b/Lib/test/test_pathlib.py	Sat Aug 09 14:52:29 2014 +0700
@@ -1125,6 +1125,11 @@
         # UNC paths are never reserved
         self.assertIs(False, P('//my/share/nul/con/aux').is_reserved())
 
+    def test_forbid_embedded_nul(self):
+        P = self.cls
+        for arg in [('/foo/\0bar'), (P('/foo'), '/\0bar')]:
+            self.assertRaises(TypeError, P, *arg)
+
 
 class PurePathTest(_BasePurePathTest, unittest.TestCase):
     cls = pathlib.PurePath