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
@@ -145,6 +145,12 @@
                     self.assertEqual(rem, 0, '%s != 0 for %s' % (rem, i))
                     self.assertEqual(r1, r2, '%s != %s for %s' % (r1, r2, i))
 
+        # test None arguments (issue 11828)
+        self.checkequal(1, 'hello', 'count', 'o', -1, None)
+        self.checkequal(1, 'hello', 'count', 'l', -2, None)
+        self.checkequal(2, 'hello', 'count', 'l', None)
+        self.checkequal(0, 'hello', 'count', 'x', None, None)
+
     def test_find(self):
         self.checkequal(0, 'abcdefghiabc', 'find', 'abc')
         self.checkequal(9, 'abcdefghiabc', 'find', 'abc', 1)
@@ -940,6 +946,12 @@
 
         self.checkraises(TypeError, 'hello', 'startswith', (42,))
 
+        # test None arguments (issue 11828)
+        self.checkequal(True, 'hello', 'startswith', 'o', -1, None)
+        self.checkequal(True, 'hello', 'startswith', 'l', -2, None)
+        self.checkequal(True, 'hello', 'startswith', 'h', None)
+        self.checkequal(False, 'hello', 'startswith', 'x', None, None)
+
     def test_endswith(self):
         self.checkequal(True, 'hello', 'endswith', 'lo')
         self.checkequal(False, 'hello', 'endswith', 'he')
@@ -989,6 +1001,12 @@
 
         self.checkraises(TypeError, 'hello', 'endswith', (42,))
 
+        # test None arguments (issue 11828)
+        self.checkequal(True, 'hello', 'endswith', 'o', -1, None)
+        self.checkequal(True, 'hello', 'endswith', 'lo', -2, None)
+        self.checkequal(True, 'hello', 'endswith', 'o', None)
+        self.checkequal(False, 'hello', 'endswith', 'x', None, None)
+
     def test___contains__(self):
         self.checkequal(True, '', '__contains__', '')
         self.checkequal(True, 'abc', '__contains__', '')
diff --git a/Objects/stringlib/find.h b/Objects/stringlib/find.h
--- a/Objects/stringlib/find.h
+++ b/Objects/stringlib/find.h
@@ -97,8 +97,8 @@
 
 /*
 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 unicodeobject.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.
@@ -111,7 +111,8 @@
 
 Py_LOCAL_INLINE(int)
 _ParseTupleFinds (PyObject *args, PyObject **substring, 
-                  Py_ssize_t *start, Py_ssize_t *end) {
+                  Py_ssize_t *start, Py_ssize_t *end,
+                  int convert_first_argument_to_unicode) {
     PyObject *tmp_substring;
     Py_ssize_t tmp_start = 0;
     Py_ssize_t tmp_end = PY_SSIZE_T_MAX;
@@ -131,9 +132,12 @@
         if (!_PyEval_SliceIndex(obj_end, &tmp_end))
             return 0;
 
-    tmp_substring = PyUnicode_FromObject(tmp_substring);
-    if (!tmp_substring)
-        return 0;
+    if (convert_first_argument_to_unicode)
+    {
+      tmp_substring = PyUnicode_FromObject(tmp_substring);
+      if (!tmp_substring)
+          return 0;
+    }
 
     *start = tmp_start;
     *end = tmp_end;
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -7515,13 +7515,7 @@
     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 (!_ParseTupleFinds(args, (PyObject **)&substring, &start, &end, 1))
         return NULL;
 
     ADJUST_INDICES(start, end, self->length);
@@ -7663,7 +7657,7 @@
     Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!_ParseTupleFinds(args, &substring, &start, &end))
+    if (!_ParseTupleFinds(args, &substring, &start, &end, 1))
         return NULL;
 
     result = stringlib_find_slice(
@@ -7724,7 +7718,7 @@
     Py_ssize_t start;
     Py_ssize_t end;
 
-    if (!_ParseTupleFinds(args, &substring, &start, &end))
+    if (!_ParseTupleFinds(args, &substring, &start, &end, 1))
         return NULL;
 
     result = stringlib_find_slice(
@@ -8588,7 +8582,7 @@
     Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!_ParseTupleFinds(args, &substring, &start, &end))
+    if (!_ParseTupleFinds(args, &substring, &start, &end, 1))
         return NULL;
 
     result = stringlib_rfind_slice(
@@ -8615,7 +8609,7 @@
     Py_ssize_t end;
     Py_ssize_t result;
 
-    if (!_ParseTupleFinds(args, &substring, &start, &end))
+    if (!_ParseTupleFinds(args, &substring, &start, &end, 1))
         return NULL;
 
     result = stringlib_rfind_slice(
@@ -9083,9 +9077,9 @@
     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 (!_ParseTupleFinds(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 +9123,9 @@
     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 (!_ParseTupleFinds(args, &subobj, &start, &end, 0))
+        return NULL;
+
     if (PyTuple_Check(subobj)) {
         Py_ssize_t i;
         for (i = 0; i < PyTuple_GET_SIZE(subobj); i++) {