diff --git a/Lib/pickletools.py b/Lib/pickletools.py
index 1b6967ae463..ca09c03460c 100644
--- a/Lib/pickletools.py
+++ b/Lib/pickletools.py
@@ -1858,7 +1858,7 @@ def optimize(p):
         s.append(p[i:j])
         i = stop
     s.append(p[i:])
-    return ''.join(s)
+    return b''.join(s)
 
 ##############################################################################
 # A symbolic pickle disassembler.
diff --git a/Lib/test/test_pickletools.py b/Lib/test/test_pickletools.py
index 2e2fe50b042..3e5b35ab588 100644
--- a/Lib/test/test_pickletools.py
+++ b/Lib/test/test_pickletools.py
@@ -1,3 +1,24 @@
+import pickle
 import pickletools
 from test import test_support
-test_support.run_doctest(pickletools)
+from test.pickletester import AbstractPickleTests
+from test.pickletester import AbstractPickleModuleTests
+
+class OptimizedPickleTests(AbstractPickleTests, AbstractPickleModuleTests):
+
+    def dumps(self, arg, proto=0, fast=0):
+        return pickletools.optimize(pickle.dumps(arg, proto))
+
+    def loads(self, buf):
+        return pickle.loads(buf)
+
+    module = pickle
+    error = KeyError
+
+def test_main():
+    test_support.run_unittest(OptimizedPickleTests)
+    test_support.run_doctest(pickletools)
+
+
+if __name__ == "__main__":
+    test_main()
diff --git a/Lib/test/test_tarfile.py b/Lib/test/test_tarfile.py
index 91cf02469a9..2fbb51e6add 100644
--- a/Lib/test/test_tarfile.py
+++ b/Lib/test/test_tarfile.py
@@ -207,6 +207,15 @@ class MiscReadTest(ReadTest):
         self.assert_(tarinfo.type == tarfile.DIRTYPE,
                 "v7 dirtype failed")
 
+    def test_xstar_type(self):
+        # The xstar format stores extra atime and ctime fields inside the
+        # space reserved for the prefix field. The prefix field must be
+        # ignored in this case, otherwise it will mess up the name.
+        try:
+            self.tar.getmember("misc/regtype-xstar")
+        except KeyError:
+            self.fail("failed to find misc/regtype-xstar (mangled prefix?)")
+
     def test_check_members(self):
         for tarinfo in self.tar:
             self.assert_(int(tarinfo.mtime) == 0o7606136617,
diff --git a/Lib/test/testtar.tar b/Lib/test/testtar.tar
index 3529bdf0acf..b5bb46b16e6 100644
Binary files a/Lib/test/testtar.tar and b/Lib/test/testtar.tar differ