diff --git a/Lib/pathlib.py b/Lib/pathlib.py
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -529,7 +529,10 @@
             return len(self._parts)
 
     def __getitem__(self, idx):
-        if idx < 0 or idx >= len(self):
+        length = len(self)
+        if idx < 0:
+            idx += length
+        if idx < 0 or idx >= length:
             raise IndexError(idx)
         return self._pathcls._from_parsed_parts(self._drv, self._root,
                                                 self._parts[:-idx - 1])
diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
--- a/Lib/test/test_pathlib.py
+++ b/Lib/test/test_pathlib.py
@@ -407,8 +407,9 @@
         self.assertEqual(par[1], P('a'))
         self.assertEqual(par[2], P('.'))
         self.assertEqual(list(par), [P('a/b'), P('a'), P('.')])
+        self.assertEqual(par[-2], P('a'))
         with self.assertRaises(IndexError):
-            par[-1]
+            par[-len(par)-1]
         with self.assertRaises(IndexError):
             par[3]
         with self.assertRaises(TypeError):