# HG changeset patch
# Parent b466fd273625560232a3b966757d916777a0f164
diff --git a/Lib/pathlib.py b/Lib/pathlib.py
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -64,10 +64,10 @@
             if sep in rel:
                 for x in reversed(rel.split(sep)):
                     if x and x != '.':
-                        parsed.append(sys.intern(x))
+                        parsed.append(sys.intern(x) if type(x) is str else x)
             else:
                 if rel and rel != '.':
-                    parsed.append(sys.intern(rel))
+                    parsed.append(sys.intern(rel) if type(rel) is str else rel)
             if drv or root:
                 if not drv:
                     # If no drive is present, try to find one in the previous
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
@@ -197,6 +197,13 @@
         self.assertEqual(P(P('a'), 'b'), P('a/b'))
         self.assertEqual(P(P('a'), P('b')), P('a/b'))
 
+    def test_constructor_subclass(self):
+        P = self.cls
+        StrSubclass = type("StrSubclass", (str,), {})
+        self.assertEqual(P(StrSubclass('a')), P('a'))
+        self.assertEqual(P(StrSubclass('a/b')), P('a/b'))
+        self.assertEqual(P(StrSubclass('/a/b')), P('/a/b'))
+
     def test_join_common(self):
         P = self.cls
         p = P('a/b')