diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index 783d544..2a14c46 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -1805,6 +1805,12 @@
 Wherever one of these methods needs to interpret the bytes as characters
 (e.g. the :func:`is...` methods), the ASCII character set is assumed.
 
+.. versionadded:: 3.3
+   The functions :func:`count`, :func:`find`, :func:`index`,
+   :func:`rfind` and :func:`rindex` have additional semantics compared to
+   the corresponding string functions: They also accept an integer in
+   range 0 to 255 (a byte) as their first argument.
+
 .. note::
 
    The methods on bytes and bytearray objects don't accept strings as their
diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
index 049929c..43ecf2a 100644
--- a/Lib/test/string_tests.py
+++ b/Lib/test/string_tests.py
@@ -28,6 +28,11 @@
     # Change in subclasses to change the behaviour of fixtesttype()
     type2test = None
 
+    # Whether the "contained items" of the container are integers in
+    # range(0, 256) (i.e. bytes, bytearray) or strings of length 1
+    # (str)
+    contains_bytes = False
+
     # All tests pass their arguments to the testing methods
     # as str objects. fixtesttype() can be used to propagate
     # these arguments to the appropriate type
@@ -117,7 +122,11 @@
         self.checkequal(0, '', 'count', 'xx', sys.maxsize, 0)
 
         self.checkraises(TypeError, 'hello', 'count')
-        self.checkraises(TypeError, 'hello', 'count', 42)
+
+        if self.contains_bytes:
+            self.checkequal(0, 'hello', 'count', 42)
+        else:
+            self.checkraises(TypeError, 'hello', 'count', 42)
 
         # For a variety of combinations,
         #    verify that str.count() matches an equivalent function
@@ -163,7 +172,11 @@
         self.checkequal( 2, 'rrarrrrrrrrra', 'find', 'a', None, 6)
 
         self.checkraises(TypeError, 'hello', 'find')
-        self.checkraises(TypeError, 'hello', 'find', 42)
+
+        if self.contains_bytes:
+            self.checkequal(-1, 'hello', 'find', 42)
+        else:
+            self.checkraises(TypeError, 'hello', 'find', 42)
 
         self.checkequal(0, '', 'find', '')
         self.checkequal(-1, '', 'find', '', 1, 1)
@@ -217,7 +230,11 @@
         self.checkequal( 2, 'rrarrrrrrrrra', 'rfind', 'a', None, 6)
 
         self.checkraises(TypeError, 'hello', 'rfind')
-        self.checkraises(TypeError, 'hello', 'rfind', 42)
+
+        if self.contains_bytes:
+            self.checkequal(-1, 'hello', 'rfind', 42)
+        else:
+            self.checkraises(TypeError, 'hello', 'rfind', 42)
 
         # For a variety of combinations,
         #    verify that str.rfind() matches __contains__
@@ -264,7 +281,11 @@
         self.checkequal( 2, 'rrarrrrrrrrra', 'index', 'a', None, 6)
 
         self.checkraises(TypeError, 'hello', 'index')
-        self.checkraises(TypeError, 'hello', 'index', 42)
+
+        if self.contains_bytes:
+            self.checkraises(ValueError, 'hello', 'index', 42)
+        else:
+            self.checkraises(TypeError, 'hello', 'index', 42)
 
     def test_rindex(self):
         self.checkequal(12, 'abcdefghiabc', 'rindex', '')
@@ -286,7 +307,11 @@
         self.checkequal( 2, 'rrarrrrrrrrra', 'rindex', 'a', None, 6)
 
         self.checkraises(TypeError, 'hello', 'rindex')
-        self.checkraises(TypeError, 'hello', 'rindex', 42)
+
+        if self.contains_bytes:
+            self.checkraises(ValueError, 'hello', 'rindex', 42)
+        else:
+            self.checkraises(TypeError, 'hello', 'rindex', 42)
 
     def test_lower(self):
         self.checkequal('hello', 'HeLLo', 'lower')
diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
index d32a44b..7acfde5 100644
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -293,10 +293,27 @@
 
     def test_count(self):
         b = self.type2test(b'mississippi')
+        i = 105
+        p = 112
+        w = 119
+
         self.assertEqual(b.count(b'i'), 4)
         self.assertEqual(b.count(b'ss'), 2)
         self.assertEqual(b.count(b'w'), 0)
 
+        self.assertEqual(b.count(i), 4)
+        self.assertEqual(b.count(w), 0)
+
+        self.assertEqual(b.count(b'i', 6), 2)
+        self.assertEqual(b.count(b'p', 6), 2)
+        self.assertEqual(b.count(b'i', 1, 3), 1)
+        self.assertEqual(b.count(b'p', 7, 9), 1)
+
+        self.assertEqual(b.count(i, 6), 2)
+        self.assertEqual(b.count(p, 6), 2)
+        self.assertEqual(b.count(i, 1, 3), 1)
+        self.assertEqual(b.count(p, 7, 9), 1)
+
     def test_startswith(self):
         b = self.type2test(b'hello')
         self.assertFalse(self.type2test().startswith(b"anything"))
@@ -327,35 +344,81 @@
 
     def test_find(self):
         b = self.type2test(b'mississippi')
+        i = 105
+        w = 119
+
         self.assertEqual(b.find(b'ss'), 2)
-        self.assertEqual(b.find(b'ss', 3), 5)
-        self.assertEqual(b.find(b'ss', 1, 7), 2)
-        self.assertEqual(b.find(b'ss', 1, 3), -1)
         self.assertEqual(b.find(b'w'), -1)
         self.assertEqual(b.find(b'mississippian'), -1)
 
+        self.assertEqual(b.find(i), 1)
+        self.assertEqual(b.find(w), -1)
+
+        self.assertEqual(b.find(b'ss', 3), 5)
+        self.assertEqual(b.find(b'ss', 1, 7), 2)
+        self.assertEqual(b.find(b'ss', 1, 3), -1)
+
+        self.assertEqual(b.find(i, 6), 7)
+        self.assertEqual(b.find(i, 1, 3), 1)
+        self.assertEqual(b.find(w, 1, 3), -1)
+
     def test_rfind(self):
         b = self.type2test(b'mississippi')
+        i = 105
+        w = 119
+
         self.assertEqual(b.rfind(b'ss'), 5)
-        self.assertEqual(b.rfind(b'ss', 3), 5)
-        self.assertEqual(b.rfind(b'ss', 0, 6), 2)
         self.assertEqual(b.rfind(b'w'), -1)
         self.assertEqual(b.rfind(b'mississippian'), -1)
 
+        self.assertEqual(b.rfind(i), 10)
+        self.assertEqual(b.rfind(w), -1)
+
+        self.assertEqual(b.rfind(b'ss', 3), 5)
+        self.assertEqual(b.rfind(b'ss', 0, 6), 2)
+
+        self.assertEqual(b.rfind(i, 1, 3), 1)
+        self.assertEqual(b.rfind(i, 3, 9), 7)
+        self.assertEqual(b.rfind(w, 1, 3), -1)
+
     def test_index(self):
-        b = self.type2test(b'world')
-        self.assertEqual(b.index(b'w'), 0)
-        self.assertEqual(b.index(b'orl'), 1)
-        self.assertRaises(ValueError, b.index, b'worm')
-        self.assertRaises(ValueError, b.index, b'ldo')
+        b = self.type2test(b'mississippi')
+        i = 105
+        w = 119
+
+        self.assertEqual(b.index(b'ss'), 2)
+        self.assertRaises(ValueError, b.index, b'w')
+        self.assertRaises(ValueError, b.index, b'mississippian')
+
+        self.assertEqual(b.index(i), 1)
+        self.assertRaises(ValueError, b.index, w)
+
+        self.assertEqual(b.index(b'ss', 3), 5)
+        self.assertEqual(b.index(b'ss', 1, 7), 2)
+        self.assertRaises(ValueError, b.index, b'ss', 1, 3)
+
+        self.assertEqual(b.index(i, 6), 7)
+        self.assertEqual(b.index(i, 1, 3), 1)
+        self.assertRaises(ValueError, b.index, w, 1, 3)
 
     def test_rindex(self):
-        # XXX could be more rigorous
-        b = self.type2test(b'world')
-        self.assertEqual(b.rindex(b'w'), 0)
-        self.assertEqual(b.rindex(b'orl'), 1)
-        self.assertRaises(ValueError, b.rindex, b'worm')
-        self.assertRaises(ValueError, b.rindex, b'ldo')
+        b = self.type2test(b'mississippi')
+        i = 105
+        w = 119
+
+        self.assertEqual(b.rindex(b'ss'), 5)
+        self.assertRaises(ValueError, b.rindex, b'w')
+        self.assertRaises(ValueError, b.rindex, b'mississippian')
+
+        self.assertEqual(b.rindex(i), 10)
+        self.assertRaises(ValueError, b.rindex, w)
+
+        self.assertEqual(b.rindex(b'ss', 3), 5)
+        self.assertEqual(b.rindex(b'ss', 0, 6), 2)
+
+        self.assertEqual(b.rindex(i, 1, 3), 1)
+        self.assertEqual(b.rindex(i, 3, 9), 7)
+        self.assertRaises(ValueError, b.rindex, w, 1, 3)
 
     def test_replace(self):
         b = self.type2test(b'mississippi')
@@ -552,6 +615,14 @@
         self.assertEqual(True, b.startswith(h, None, -2))
         self.assertEqual(False, b.startswith(x, None, None))
 
+    def test_integer_arguments_out_of_byte_range(self):
+        b = self.type2test(b'hello')
+
+        for method in (b.count, b.find, b.index, b.rfind, b.rindex):
+            self.assertRaises(ValueError, method, -1)
+            self.assertRaises(ValueError, method, 256)
+            self.assertRaises(ValueError, method, 9999)
+
     def test_find_etc_raise_correct_error_messages(self):
         # issue 11828
         b = self.type2test(b'hello')
@@ -1161,9 +1232,11 @@
 
 class ByteArrayAsStringTest(FixedStringTest):
     type2test = bytearray
+    contains_bytes = True
 
 class BytesAsStringTest(FixedStringTest):
     type2test = bytes
+    contains_bytes = True
 
 
 class SubclassTest(unittest.TestCase):
diff --git a/Misc/NEWS b/Misc/NEWS
index bfd97cb..7fe6143 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,10 @@
 Core and Builtins
 -----------------
 
+- Issue #12170: The count(), find(), rfind(), index() and rindex() methods
+  of bytes and bytearray objects now accept an integer between 0 and 255
+  as their first argument.  Patch by Petri Lehtinen.
+
 - Issue #12604: VTRACE macro expanded to no-op in _sre.c to avoid compiler
   warnings. Patch by Josh Triplett and Petri Lehtinen.
 
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
index 0c9add0..6f0b28d 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -1071,24 +1071,41 @@
 bytearray_find_internal(PyByteArrayObject *self, PyObject *args, int dir)
 {
     PyObject *subobj;
+    char byte;
     Py_buffer subbuf;
+    const char *sub;
+    Py_ssize_t sub_len;
     Py_ssize_t start=0, end=PY_SSIZE_T_MAX;
     Py_ssize_t res;
 
-    if (!stringlib_parse_args_finds("find/rfind/index/rindex",
-                                    args, &subobj, &start, &end))
+    if (!stringlib_parse_args_finds_byte("find/rfind/index/rindex",
+                                         args, &subobj, &byte, &start, &end))
         return -2;
-    if (_getbuffer(subobj, &subbuf) < 0)
-        return -2;
+
+    if (subobj) {
+        if (_getbuffer(subobj, &subbuf) < 0)
+            return -2;
+
+        sub = subbuf.buf;
+        sub_len = subbuf.len;
+    }
+    else {
+        sub = &byte;
+        sub_len = 1;
+    }
+
     if (dir > 0)
         res = stringlib_find_slice(
             PyByteArray_AS_STRING(self), PyByteArray_GET_SIZE(self),
-            subbuf.buf, subbuf.len, start, end);
+            sub, sub_len, start, end);
     else
         res = stringlib_rfind_slice(
             PyByteArray_AS_STRING(self), PyByteArray_GET_SIZE(self),
-            subbuf.buf, subbuf.len, start, end);
-    PyBuffer_Release(&subbuf);
+            sub, sub_len, start, end);
+
+    if (subobj)
+        PyBuffer_Release(&subbuf);
+
     return res;
 }
 
@@ -1121,23 +1138,39 @@
 bytearray_count(PyByteArrayObject *self, PyObject *args)
 {
     PyObject *sub_obj;
-    const char *str = PyByteArray_AS_STRING(self);
+    const char *str = PyByteArray_AS_STRING(self), *sub;
+    Py_ssize_t sub_len;
+    char byte;
     Py_ssize_t start = 0, end = PY_SSIZE_T_MAX;
+
     Py_buffer vsub;
     PyObject *count_obj;
 
-    if (!stringlib_parse_args_finds("count", args, &sub_obj, &start, &end))
+    if (!stringlib_parse_args_finds_byte("count", args, &sub_obj, &byte,
+                                         &start, &end))
         return NULL;
 
-    if (_getbuffer(sub_obj, &vsub) < 0)
-        return NULL;
+    if (sub_obj) {
+        if (_getbuffer(sub_obj, &vsub) < 0)
+            return NULL;
+
+        sub = vsub.buf;
+        sub_len = vsub.len;
+    }
+    else {
+        sub = &byte;
+        sub_len = 1;
+    }
 
     ADJUST_INDICES(start, end, PyByteArray_GET_SIZE(self));
 
     count_obj = PyLong_FromSsize_t(
-        stringlib_count(str + start, end - start, vsub.buf, vsub.len, PY_SSIZE_T_MAX)
+        stringlib_count(str + start, end - start, sub, sub_len, PY_SSIZE_T_MAX)
         );
-    PyBuffer_Release(&vsub);
+
+    if (sub_obj)
+        PyBuffer_Release(&vsub);
+
     return count_obj;
 }
 
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index 17e31b9..7438a70 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -1230,31 +1230,42 @@
 bytes_find_internal(PyBytesObject *self, PyObject *args, int dir)
 {
     PyObject *subobj;
+    char byte;
+    Py_buffer subbuf;
     const char *sub;
     Py_ssize_t sub_len;
     Py_ssize_t start=0, end=PY_SSIZE_T_MAX;
+    Py_ssize_t res;
 
-    if (!stringlib_parse_args_finds("find/rfind/index/rindex",
-                                    args, &subobj, &start, &end))
+    if (!stringlib_parse_args_finds_byte("find/rfind/index/rindex",
+                                         args, &subobj, &byte, &start, &end))
         return -2;
 
-    if (PyBytes_Check(subobj)) {
-        sub = PyBytes_AS_STRING(subobj);
-        sub_len = PyBytes_GET_SIZE(subobj);
+    if (subobj) {
+        if (_getbuffer(subobj, &subbuf) < 0)
+            return -2;
+
+        sub = subbuf.buf;
+        sub_len = subbuf.len;
     }
-    else if (PyObject_AsCharBuffer(subobj, &sub, &sub_len))
-        /* XXX - the "expected a character buffer object" is pretty
-           confusing for a non-expert.  remap to something else ? */
-        return -2;
+    else {
+        sub = &byte;
+        sub_len = 1;
+    }
 
     if (dir > 0)
-        return stringlib_find_slice(
+        res = stringlib_find_slice(
             PyBytes_AS_STRING(self), PyBytes_GET_SIZE(self),
             sub, sub_len, start, end);
     else
-        return stringlib_rfind_slice(
+        res = stringlib_rfind_slice(
             PyBytes_AS_STRING(self), PyBytes_GET_SIZE(self),
             sub, sub_len, start, end);
+
+    if (subobj)
+        PyBuffer_Release(&subbuf);
+
+    return res;
 }
 
 
@@ -1480,23 +1491,38 @@
     PyObject *sub_obj;
     const char *str = PyBytes_AS_STRING(self), *sub;
     Py_ssize_t sub_len;
+    char byte;
     Py_ssize_t start = 0, end = PY_SSIZE_T_MAX;
 
-    if (!stringlib_parse_args_finds("count", args, &sub_obj, &start, &end))
+    Py_buffer vsub;
+    PyObject *count_obj;
+
+    if (!stringlib_parse_args_finds_byte("count", args, &sub_obj, &byte,
+                                         &start, &end))
         return NULL;
 
-    if (PyBytes_Check(sub_obj)) {
-        sub = PyBytes_AS_STRING(sub_obj);
-        sub_len = PyBytes_GET_SIZE(sub_obj);
+    if (sub_obj) {
+        if (_getbuffer(sub_obj, &vsub) < 0)
+            return NULL;
+
+        sub = vsub.buf;
+        sub_len = vsub.len;
     }
-    else if (PyObject_AsCharBuffer(sub_obj, &sub, &sub_len))
-        return NULL;
+    else {
+        sub = &byte;
+        sub_len = 1;
+    }
 
     ADJUST_INDICES(start, end, PyBytes_GET_SIZE(self));
 
-    return PyLong_FromSsize_t(
+    count_obj = PyLong_FromSsize_t(
         stringlib_count(str + start, end - start, sub, sub_len, PY_SSIZE_T_MAX)
         );
+
+    if (sub_obj)
+        PyBuffer_Release(&vsub);
+
+    return count_obj;
 }
 
 
diff --git a/Objects/stringlib/find.h b/Objects/stringlib/find.h
index 7cce156..00eaf1b 100644
--- a/Objects/stringlib/find.h
+++ b/Objects/stringlib/find.h
@@ -167,4 +167,47 @@
     return 0;
 }
 
+#else /* !STRINGLIB_IS_UNICODE */
+
+/*
+Wraps stringlib_parse_args_finds() and additionally checks whether the
+first argument is an integer in range(0, 256).
+
+If this is the case, writes the integer value to the byte parameter
+and sets subobj to NULL. Otherwise, sets the first argument to subobj
+and doesn't touch byte. The other parameters are similar to those of
+stringlib_parse_args_finds().
+*/
+
+Py_LOCAL_INLINE(int)
+STRINGLIB(parse_args_finds_byte)(const char *function_name, PyObject *args,
+                                 PyObject **subobj, char *byte,
+                                 Py_ssize_t *start, Py_ssize_t *end)
+{
+    PyObject *tmp_subobj;
+    Py_ssize_t ival;
+
+    if(!STRINGLIB(parse_args_finds)(function_name, args, &tmp_subobj,
+                                    start, end))
+        return 0;
+
+    ival = PyNumber_AsSsize_t(tmp_subobj, PyExc_ValueError);
+    if (ival == -1 && PyErr_Occurred()) {
+        PyErr_Clear();
+        *subobj = tmp_subobj;
+    }
+    else {
+        /* The first argument was an integer */
+        if(ival < 0 || ival > 255) {
+            PyErr_SetString(PyExc_ValueError, "byte must be in range(0, 256)");
+            return 0;
+        }
+
+        *subobj = NULL;
+        *byte = (char)ival;
+    }
+
+    return 1;
+}
+
 #endif /* STRINGLIB_IS_UNICODE */