Index: Lib/test/test_fileio.py
===================================================================
--- Lib/test/test_fileio.py	(revision 81462)
+++ Lib/test/test_fileio.py	(working copy)
@@ -80,6 +80,9 @@
         self.assertEqual(self.f.readline(None), b"hi\n")
         self.assertEqual(self.f.readlines(None), [b"bye\n", b"abc"])
 
+    def testWriteUnicode(self):
+        self.assertRaises(TypeError, self.f.write, '')
+
     def testRepr(self):
         self.assertEquals(repr(self.f), "<_io.FileIO name=%r mode='%s'>"
                                         % (self.f.name, self.f.mode))
@@ -172,7 +175,7 @@
 
     @ClosedFDRaises
     def testErrnoOnClosedWrite(self, f):
-        f.write('a')
+        f.write(b'a')
 
     @ClosedFDRaises
     def testErrnoOnClosedSeek(self, f):
Index: Modules/_io/fileio.c
===================================================================
--- Modules/_io/fileio.c	(revision 81462)
+++ Modules/_io/fileio.c	(working copy)
@@ -648,12 +648,20 @@
 {
     Py_buffer pbuf;
     Py_ssize_t n;
+    PyObject *obj;
 
     if (self->fd < 0)
         return err_closed();
     if (!self->writable)
         return err_mode("writing");
 
+    if (!PyArg_ParseTuple(args, "O", &obj))
+        return NULL;
+    if (PyUnicode_Check(obj)){
+        PyErr_SetString(PyExc_TypeError, "must not be unicode!");
+        return NULL;
+    }
+
     if (!PyArg_ParseTuple(args, "s*", &pbuf))
         return NULL;
 
Index: Modules/_io/bufferedio.c
===================================================================
--- Modules/_io/bufferedio.c	(revision 81462)
+++ Modules/_io/bufferedio.c	(working copy)
@@ -1693,8 +1693,16 @@
     Py_buffer buf;
     Py_ssize_t written, avail, remaining;
     Py_off_t offset;
+    PyObject *obj;
 
     CHECK_INITIALIZED(self)
+    if (!PyArg_ParseTuple(args, "O", &obj))
+        return NULL;
+    if (PyUnicode_Check(obj)){
+        PyErr_SetString(PyExc_TypeError, "must not be unicode!");
+        return NULL;
+    }
+
     if (!PyArg_ParseTuple(args, "s*:write", &buf)) {
         return NULL;
     }