diff -r c6df85e1d42e Lib/test/test_io.py
--- a/Lib/test/test_io.py	Tue Apr 14 13:54:09 2015 -0700
+++ b/Lib/test/test_io.py	Sun Apr 26 22:50:16 2015 -0700
@@ -722,10 +722,10 @@
 @support.cpython_only
 class APIMismatchTest(unittest.TestCase):
 
-    @unittest.expectedFailure  # Test to be fixed by issue9858.
     def test_RawIOBase_io_in_pyio_match(self):
         """Test that pyio RawIOBase class has all c RawIOBase methods"""
-        mismatch = support.detect_api_mismatch(pyio.RawIOBase, io.RawIOBase)
+        mismatch = support.detect_api_mismatch(pyio.RawIOBase, io.RawIOBase,
+                                               ignore=('__weakref__',))
         self.assertEqual(mismatch, set(), msg='Python RawIOBase does not have all C RawIOBase methods')
 
     def test_RawIOBase_pyio_in_io_match(self):
diff -r c6df85e1d42e Modules/_io/iobase.c
--- a/Modules/_io/iobase.c	Tue Apr 14 13:54:09 2015 -0700
+++ b/Modules/_io/iobase.c	Sun Apr 26 22:50:16 2015 -0700
@@ -892,9 +892,25 @@
     return result;
 }
 
+static PyObject *
+rawiobase_readinto(PyObject *self, PyObject *args)
+{
+    PyErr_SetString(PyExc_NotImplementedError, "Not Implemented in c");
+    return NULL;
+}
+
+static PyObject *
+rawiobase_write(PyObject *self, PyObject *args)
+{
+    PyErr_SetString(PyExc_NotImplementedError, "Not Implemented in c");
+    return NULL;
+}
+
 static PyMethodDef rawiobase_methods[] = {
     {"read", rawiobase_read, METH_VARARGS},
     {"readall", rawiobase_readall, METH_NOARGS, rawiobase_readall_doc},
+    {"readinto", rawiobase_readinto, METH_VARARGS,},
+    {"write", rawiobase_write, METH_VARARGS,},
     {NULL, NULL}
 };