diff -r 3544827d42e6 Lib/_pyio.py
--- a/Lib/_pyio.py	Tue Jan 28 12:26:24 2014 -0500
+++ b/Lib/_pyio.py	Tue Jan 28 22:25:01 2014 +0200
@@ -2052,7 +2052,7 @@
     def __init__(self, initial_value="", newline="\n"):
         super(StringIO, self).__init__(BytesIO(),
                                        encoding="utf-8",
-                                       errors="strict",
+                                       errors="surrogatepass",
                                        newline=newline)
         # Issue #5645: make universal newlines semantics the same as in the
         # C version, even under Windows.
diff -r 3544827d42e6 Lib/test/test_memoryio.py
--- a/Lib/test/test_memoryio.py	Tue Jan 28 12:26:24 2014 -0500
+++ b/Lib/test/test_memoryio.py	Tue Jan 28 22:25:01 2014 +0200
@@ -609,6 +609,13 @@
     UnsupportedOperation = pyio.UnsupportedOperation
     EOF = ""
 
+    def test_lone_surrogates(self):
+        memio = self.ioclass('\ud800')
+        self.assertEqual(memio.read(), '\ud800')
+        memio = self.ioclass()
+        memio.write('\ud800')
+        self.assertEqual(memio.getvalue(), '\ud800')
+
 
 class PyStringIOPickleTest(TextIOTestMixin, unittest.TestCase):
     """Test if pickle restores properly the internal state of StringIO.