diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
--- a/Lib/test/string_tests.py
+++ b/Lib/test/string_tests.py
@@ -1183,6 +1183,63 @@
         self.checkraises(ValueError, S, 'rpartition', '')
         self.checkraises(TypeError, S, 'rpartition', None)
 
+    def test_none_arguments(self):
+        # issue 11828
+        s = 'hello'
+        self.checkequal(2, s, 'find', 'l', None)
+        self.checkequal(3, s, 'find', 'l', -2, None)
+        self.checkequal(2, s, 'find', 'l', None, -2)
+        self.checkequal(0, s, 'find', 'h', None, None)
+
+        self.checkequal(3, s, 'rfind', 'l', None)
+        self.checkequal(3, s, 'rfind', 'l', -2, None)
+        self.checkequal(2, s, 'rfind', 'l', None, -2)
+        self.checkequal(0, s, 'rfind', 'h', None, None)
+
+        self.checkequal(2, s, 'index', 'l', None)
+        self.checkequal(3, s, 'index', 'l', -2, None)
+        self.checkequal(2, s, 'index', 'l', None, -2)
+        self.checkequal(0, s, 'index', 'h', None, None)
+
+        self.checkequal(3, s, 'rindex', 'l', None)
+        self.checkequal(3, s, 'rindex', 'l', -2, None)
+        self.checkequal(2, s, 'rindex', 'l', None, -2)
+        self.checkequal(0, s, 'rindex', 'h', None, None)
+
+        self.checkequal(2, s, 'count', 'l', None)
+        self.checkequal(1, s, 'count', 'l', -2, None)
+        self.checkequal(1, s, 'count', 'l', None, -2)
+        self.checkequal(0, s, 'count', 'x', None, None)
+
+        self.checkequal(True, s, 'endswith', 'o', None)
+        self.checkequal(True, s, 'endswith', 'lo', -2, None)
+        self.checkequal(True, s, 'endswith', 'l', None, -2)
+        self.checkequal(False, s, 'endswith', 'x', None, None)
+
+        self.checkequal(True, s, 'startswith', 'h', None)
+        self.checkequal(True, s, 'startswith', 'l', -2, None)
+        self.checkequal(True, s, 'startswith', 'h', None, -2)
+        self.checkequal(False, s, 'startswith', 'x', None, None)
+
+    def test_find_etc_raise_correct_error_messages(self):
+        # issue 11828
+        s = 'hello'
+        x = 'x'
+        self.assertRaisesRegexp(TypeError, r'^find\(', s.find,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'^rfind\(', s.rfind,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'^index\(', s.index,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'^rindex\(', s.rindex,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'^count\(', s.count,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'^startswith\(', s.startswith,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'^endswith\(', s.endswith,
+                                x, None, None, None)
+
 
 class MixinStrUnicodeTest:
     # Additional tests that only work with str and unicode.
diff --git a/Lib/test/test_bytes.py b/Lib/test/test_bytes.py
--- a/Lib/test/test_bytes.py
+++ b/Lib/test/test_bytes.py
@@ -478,6 +478,68 @@
         self.assertRaises(ValueError, self.type2test.maketrans, b'abc', b'xyzq')
         self.assertRaises(TypeError, self.type2test.maketrans, 'abc', 'def')
 
+    def test_none_arguments(self):
+        # issue 11828
+        b = self.type2test(b'hello')
+        l = self.type2test(b'l')
+        h = self.type2test(b'h')
+        x = self.type2test(b'x')
+        o = self.type2test(b'o')
+
+        self.assertEqual(2, b.find(l, None))
+        self.assertEqual(3, b.find(l, -2, None))
+        self.assertEqual(2, b.find(l, None, -2))
+        self.assertEqual(0, b.find(h, None, None))
+
+        self.assertEqual(3, b.rfind(l, None))
+        self.assertEqual(3, b.rfind(l, -2, None))
+        self.assertEqual(2, b.rfind(l, None, -2))
+        self.assertEqual(0, b.rfind(h, None, None))
+
+        self.assertEqual(2, b.index(l, None))
+        self.assertEqual(3, b.index(l, -2, None))
+        self.assertEqual(2, b.index(l, None, -2))
+        self.assertEqual(0, b.index(h, None, None))
+
+        self.assertEqual(3, b.rindex(l, None))
+        self.assertEqual(3, b.rindex(l, -2, None))
+        self.assertEqual(2, b.rindex(l, None, -2))
+        self.assertEqual(0, b.rindex(h, None, None))
+
+        self.assertEqual(2, b.count(l, None))
+        self.assertEqual(1, b.count(l, -2, None))
+        self.assertEqual(1, b.count(l, None, -2))
+        self.assertEqual(0, b.count(x, None, None))
+
+        self.assertEqual(True, b.endswith(o, None))
+        self.assertEqual(True, b.endswith(o, -2, None))
+        self.assertEqual(True, b.endswith(l, None, -2))
+        self.assertEqual(False, b.endswith(x, None, None))
+
+        self.assertEqual(True, b.startswith(h, None))
+        self.assertEqual(True, b.startswith(l, -2, None))
+        self.assertEqual(True, b.startswith(h, None, -2))
+        self.assertEqual(False, b.startswith(x, None, None))
+
+    def test_find_etc_raise_correct_error_messages(self):
+        # issue 11828
+        b = self.type2test(b'hello')
+        x = self.type2test(b'x')
+        self.assertRaisesRegexp(TypeError, r'\bfind\b', b.find,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'\brfind\b', b.rfind,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'\bindex\b', b.index,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'\brindex\b', b.rindex,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'\bcount\b', b.count,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'\bstartswith\b', b.startswith,
+                                x, None, None, None)
+        self.assertRaisesRegexp(TypeError, r'\bendswith\b', b.endswith,
+                                x, None, None, None)
+
 
 class BytesTest(BaseBytesTest):
     type2test = bytes
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -1081,9 +1081,10 @@
     Py_ssize_t start=0, end=PY_SSIZE_T_MAX;
     Py_ssize_t res;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:find/rfind/index/rindex", &subobj,
-        _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+    if (!stringlib_parse_tuple_finds("find/rfind/index/rindex", args, &subobj,
+                                     &start, &end, 0))
         return -2;
+
     if (_getbuffer(subobj, &subbuf) < 0)
         return -2;
     if (dir > 0)
@@ -1132,8 +1133,7 @@
     Py_buffer vsub;
     PyObject *count_obj;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:count", &sub_obj,
-        _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+    if (!stringlib_parse_tuple_finds("count", args, &sub_obj, &start, &end, 0))
         return NULL;
 
     if (_getbuffer(sub_obj, &vsub) < 0)
@@ -1315,9 +1315,10 @@
     PyObject *subobj;
     int result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:startswith", &subobj,
-        _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+    if (!stringlib_parse_tuple_finds("startswith", args, &subobj,
+                                     &start, &end, 0))
         return NULL;
+
     if (PyTuple_Check(subobj)) {
         Py_ssize_t i;
         for (i = 0; i < PyTuple_GET_SIZE(subobj); i++) {
@@ -1355,9 +1356,10 @@
     PyObject *subobj;
     int result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:endswith", &subobj,
-        _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+    if (!stringlib_parse_tuple_finds("endswith", args, &subobj,
+                                     &start, &end, 0))
         return NULL;
+
     if (PyTuple_Check(subobj)) {
         Py_ssize_t i;
         for (i = 0; i < PyTuple_GET_SIZE(subobj); i++) {
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -1240,19 +1240,9 @@
     const char *sub;
     Py_ssize_t sub_len;
     Py_ssize_t start=0, end=PY_SSIZE_T_MAX;
-    PyObject *obj_start=Py_None, *obj_end=Py_None;
-
-    if (!PyArg_ParseTuple(args, "O|OO:find/rfind/index/rindex", &subobj,
-        &obj_start, &obj_end))
-        return -2;
-    /* To support None in "start" and "end" arguments, meaning
-       the same as if they were not passed.
-    */
-    if (obj_start != Py_None)
-        if (!_PyEval_SliceIndex(obj_start, &start))
-        return -2;
-    if (obj_end != Py_None)
-        if (!_PyEval_SliceIndex(obj_end, &end))
+
+    if (!stringlib_parse_tuple_finds("find/rfind/index/rindex", args, &subobj,
+                                     &start, &end, 0))
         return -2;
 
     if (PyBytes_Check(subobj)) {
@@ -1499,8 +1489,7 @@
     Py_ssize_t sub_len;
     Py_ssize_t start = 0, end = PY_SSIZE_T_MAX;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:count", &sub_obj,
-        _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+    if (!stringlib_parse_tuple_finds("count", args, &sub_obj, &start, &end, 0))
         return NULL;
 
     if (PyBytes_Check(sub_obj)) {
@@ -2218,9 +2207,10 @@
     PyObject *subobj;
     int result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:startswith", &subobj,
-        _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+    if (!stringlib_parse_tuple_finds("startswith", args, &subobj,
+                                     &start, &end, 0))
         return NULL;
+
     if (PyTuple_Check(subobj)) {
         Py_ssize_t i;
         for (i = 0; i < PyTuple_GET_SIZE(subobj); i++) {
@@ -2259,9 +2249,10 @@
     PyObject *subobj;
     int result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:endswith", &subobj,
-        _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
+    if (!stringlib_parse_tuple_finds("endswith", args, &subobj,
+                                     &start, &end, 0))
         return NULL;
+
     if (PyTuple_Check(subobj)) {
         Py_ssize_t i;
         for (i = 0; i < PyTuple_GET_SIZE(subobj); i++) {
diff --git a/Objects/stringlib/find.h b/Objects/stringlib/find.h
--- a/Objects/stringlib/find.h
+++ b/Objects/stringlib/find.h
@@ -93,12 +93,10 @@
 
 #endif /* STRINGLIB_WANT_CONTAINS_OBJ */
 
-#if STRINGLIB_IS_UNICODE
-
 /*
 This function is a helper for the "find" family (find, rfind, index,
-rindex) of unicodeobject.c file, because they all have the same 
-behaviour for the arguments.
+rindex, count, startswith, endswith) of {unicode,bytes,bytearray}object.c
+file, because they all have the same behaviour for the arguments.
 
 It does not touch the variables received until it knows everything 
 is ok.
@@ -110,15 +108,20 @@
 */
 
 Py_LOCAL_INLINE(int)
-_ParseTupleFinds (PyObject *args, PyObject **substring, 
-                  Py_ssize_t *start, Py_ssize_t *end) {
+stringlib_parse_tuple_finds(const char * function_name, PyObject *args,
+                            PyObject **substring, Py_ssize_t *start,
+                            Py_ssize_t *end, int convert_first_arg_to_unicode)
+{
     PyObject *tmp_substring;
     Py_ssize_t tmp_start = 0;
     Py_ssize_t tmp_end = PY_SSIZE_T_MAX;
     PyObject *obj_start=Py_None, *obj_end=Py_None;
+    char format[50] = "O|OO:";
 
-    if (!PyArg_ParseTuple(args, "O|OO:find", &tmp_substring,
-         &obj_start, &obj_end))
+    strncpy(format + 5, function_name, 44);
+    format[49] = '\0';
+
+    if (!PyArg_ParseTuple(args, format, &tmp_substring, &obj_start, &obj_end))
         return 0;
 
     /* To support None in "start" and "end" arguments, meaning
@@ -131,9 +134,11 @@
         if (!_PyEval_SliceIndex(obj_end, &tmp_end))
             return 0;
 
-    tmp_substring = PyUnicode_FromObject(tmp_substring);
-    if (!tmp_substring)
-        return 0;
+    if (convert_first_arg_to_unicode) {
+        tmp_substring = PyUnicode_FromObject(tmp_substring);
+        if (!tmp_substring)
+            return 0;
+    }
 
     *start = tmp_start;
     *end = tmp_end;
@@ -141,6 +146,4 @@
     return 1;
 }
 
-#endif /* STRINGLIB_IS_UNICODE */
-
 #endif /* STRINGLIB_FIND_H */
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -7515,13 +7515,8 @@
     Py_ssize_t end = PY_SSIZE_T_MAX;
     PyObject *result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:count", &substring,
-                          _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
-        return NULL;
-
-    substring = (PyUnicodeObject *)PyUnicode_FromObject(
-        (PyObject *)substring);
-    if (substring == NULL)
+    if (!stringlib_parse_tuple_finds("count", args, (PyObject **)&substring,
+                                     &start, &end, 1))
         return NULL;
 
     ADJUST_INDICES(start, end, self->length);
@@ -7663,7 +7658,8 @@
     Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!_ParseTupleFinds(args, &substring, &start, &end))
+    if (!stringlib_parse_tuple_finds("find", args, &substring,
+                                     &start, &end, 1))
         return NULL;
 
     result = stringlib_find_slice(
@@ -7724,7 +7720,8 @@
     Py_ssize_t start;
     Py_ssize_t end;
 
-    if (!_ParseTupleFinds(args, &substring, &start, &end))
+    if (!stringlib_parse_tuple_finds("index", args, &substring,
+                                     &start, &end, 1))
         return NULL;
 
     result = stringlib_find_slice(
@@ -8588,7 +8585,8 @@
     Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!_ParseTupleFinds(args, &substring, &start, &end))
+    if (!stringlib_parse_tuple_finds("rfind", args, &substring,
+                                     &start, &end, 1))
         return NULL;
 
     result = stringlib_rfind_slice(
@@ -8615,7 +8613,8 @@
     Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!_ParseTupleFinds(args, &substring, &start, &end))
+    if (!stringlib_parse_tuple_finds("rindex", args, &substring,
+                                     &start, &end, 1))
         return NULL;
 
     result = stringlib_rfind_slice(
@@ -9083,9 +9082,10 @@
     Py_ssize_t end = PY_SSIZE_T_MAX;
     int result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:startswith", &subobj,
-                          _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
-        return NULL;
+    if (!stringlib_parse_tuple_finds("startswith", args, &subobj,
+                                     &start, &end, 0))
+        return NULL;
+
     if (PyTuple_Check(subobj)) {
         Py_ssize_t i;
         for (i = 0; i < PyTuple_GET_SIZE(subobj); i++) {
@@ -9129,9 +9129,10 @@
     Py_ssize_t end = PY_SSIZE_T_MAX;
     int result;
 
-    if (!PyArg_ParseTuple(args, "O|O&O&:endswith", &subobj,
-                          _PyEval_SliceIndex, &start, _PyEval_SliceIndex, &end))
-        return NULL;
+    if (!stringlib_parse_tuple_finds("endswith", args, &subobj,
+                                     &start, &end, 0))
+        return NULL;
+
     if (PyTuple_Check(subobj)) {
         Py_ssize_t i;
         for (i = 0; i < PyTuple_GET_SIZE(subobj); i++) {