diff -r 670fb496f1f6 Lib/test/test_bytes.py
--- a/Lib/test/test_bytes.py	Sun May 11 23:37:26 2014 -0400
+++ b/Lib/test/test_bytes.py	Tue May 13 03:21:07 2014 +0200
@@ -13,6 +13,7 @@ import functools
 import pickle
 import tempfile
 import unittest
+import warnings
 import test.test_support
 import test.string_tests
 import test.buffer_tests
@@ -194,9 +195,9 @@ class BaseBytesTest(unittest.TestCase):
         sample = u"Hello world\n\x80\x81\xfe\xff"
         b = self.type2test(sample, "latin1")
         self.assertRaises(UnicodeDecodeError, b.decode, "utf8")
-        self.assertEqual(b.decode("utf8", "ignore"), "Hello world\n")
+        self.assertEqual(b.decode("utf8", "ignore"), u"Hello world\n")
         self.assertEqual(b.decode(errors="ignore", encoding="utf8"),
-                         "Hello world\n")
+                         u"Hello world\n")
 
     def test_from_int(self):
         b = self.type2test(0)
@@ -518,6 +519,28 @@ class BaseBytesTest(unittest.TestCase):
         self.assertRaisesRegexp(TypeError, r'\bendswith\b', b.endswith,
                                 x, None, None, None)
 
+    def test_compare(self):
+        if sys.flags.bytes_warning:
+            import contextlib
+            @contextlib.contextmanager
+            def bytes_warning():
+                with warnings.catch_warnings(record=True) as warns:
+                    warnings.simplefilter("default", BytesWarning)
+                    yield
+                self.assertEqual(len(warns), 1, warns)
+                self.assertIsInstance(warns[0], warnings.WarningMessage)
+            with bytes_warning():
+                self.type2test('') == u''
+            with bytes_warning():
+                self.type2test('') != u''
+
+            with bytes_warning():
+                u'' == self.type2test('')
+            with bytes_warning():
+                u'' != self.type2test('')
+        else:
+            self.skipTest("BytesWarning is needed for this test: use -bb option")
+
 
 class ByteArrayTest(BaseBytesTest):
     type2test = bytearray
diff -r 670fb496f1f6 Objects/bytearrayobject.c
--- a/Objects/bytearrayobject.c	Sun May 11 23:37:26 2014 -0400
+++ b/Objects/bytearrayobject.c	Tue May 13 03:21:07 2014 +0200
@@ -1029,7 +1029,7 @@ bytearray_richcompare(PyObject *self, Py
 #ifdef Py_USING_UNICODE
     if (PyObject_IsInstance(self, (PyObject*)&PyUnicode_Type) ||
         PyObject_IsInstance(other, (PyObject*)&PyUnicode_Type)) {
-        if (Py_BytesWarningFlag && op == Py_EQ) {
+        if (Py_BytesWarningFlag && (op == Py_EQ || op == Py_NE)) {
             if (PyErr_WarnEx(PyExc_BytesWarning,
                             "Comparison between bytearray and string", 1))
                 return NULL;
diff -r 670fb496f1f6 Objects/stringobject.c
--- a/Objects/stringobject.c	Sun May 11 23:37:26 2014 -0400
+++ b/Objects/stringobject.c	Tue May 13 03:21:07 2014 +0200
@@ -1197,6 +1197,15 @@ string_richcompare(PyStringObject *a, Py
 
     /* Make sure both arguments are strings. */
     if (!(PyString_Check(a) && PyString_Check(b))) {
+        if (Py_BytesWarningFlag && (op == Py_EQ || op == Py_NE) &&
+            (PyObject_IsInstance((PyObject*)a,
+                                 (PyObject*)&PyUnicode_Type) ||
+            PyObject_IsInstance((PyObject*)b,
+                                 (PyObject*)&PyUnicode_Type))) {
+            if (PyErr_WarnEx(PyExc_BytesWarning,
+                        "Comparison between bytes and string", 1))
+                return NULL;
+        }
         result = Py_NotImplemented;
         goto out;
     }
diff -r 670fb496f1f6 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Sun May 11 23:37:26 2014 -0400
+++ b/Objects/unicodeobject.c	Tue May 13 03:21:07 2014 +0200
@@ -6186,6 +6186,14 @@ int PyUnicode_Compare(PyObject *left,
     PyUnicodeObject *u = NULL, *v = NULL;
     int result;
 
+    if (Py_BytesWarningFlag
+        && (PyString_Check(left) || PyByteArray_Check(left) ||
+            PyString_Check(right) || PyByteArray_Check(right))) {
+        if (PyErr_WarnEx(PyExc_BytesWarning,
+                        "Comparison between bytearray and string", 1))
+            return -1;
+    }
+
     /* Coerce the two arguments */
     u = (PyUnicodeObject *)PyUnicode_FromObject(left);
     if (u == NULL)