diff --git a/Lib/ctypes/__init__.py b/Lib/ctypes/__init__.py
index 785bd188702..055294c414f 100644
--- a/Lib/ctypes/__init__.py
+++ b/Lib/ctypes/__init__.py
@@ -49,7 +49,7 @@ def create_string_buffer(init, size=None):
     create_string_buffer(anInteger) -> character array
     create_string_buffer(aString, anInteger) -> character array
     """
-    if isinstance(init, (str, bytes)):
+    if isinstance(init, bytes):
         if size is None:
             size = len(init)+1
         buftype = c_char * size
@@ -284,7 +284,7 @@ def create_unicode_buffer(init, size=None):
     create_unicode_buffer(anInteger) -> character array
     create_unicode_buffer(aString, anInteger) -> character array
     """
-    if isinstance(init, (str, bytes)):
+    if isinstance(init, str):
         if size is None:
             size = len(init)+1
         buftype = c_wchar * size
diff --git a/Lib/ctypes/test/test_buffers.py b/Lib/ctypes/test/test_buffers.py
index 8fa883cc528..166faaf4e4b 100644
--- a/Lib/ctypes/test/test_buffers.py
+++ b/Lib/ctypes/test/test_buffers.py
@@ -21,6 +21,8 @@ class StringBufferTestCase(unittest.TestCase):
         self.assertEqual(b[::2], b"ac")
         self.assertEqual(b[::5], b"a")
 
+        self.assertRaises(TypeError, create_string_buffer, "abc")
+
     def test_buffer_interface(self):
         self.assertEqual(len(bytearray(create_string_buffer(0))), 0)
         self.assertEqual(len(bytearray(create_string_buffer(1))), 1)
@@ -43,6 +45,8 @@ class StringBufferTestCase(unittest.TestCase):
         self.assertEqual(b[::2], "ac")
         self.assertEqual(b[::5], "a")
 
+        self.assertRaises(TypeError, create_unicode_buffer, b"abc")
+
     @need_symbol('c_wchar')
     def test_unicode_conversion(self):
         b = create_unicode_buffer("abc")
diff --git a/Lib/ctypes/test/test_bytes.py b/Lib/ctypes/test/test_bytes.py
index 363b3f84b6a..20fa0565034 100644
--- a/Lib/ctypes/test/test_bytes.py
+++ b/Lib/ctypes/test/test_bytes.py
@@ -6,27 +6,40 @@ from ctypes import *
 class BytesTest(unittest.TestCase):
     def test_c_char(self):
         x = c_char(b"x")
+        self.assertRaises(TypeError, c_char, "x")
         x.value = b"y"
+        with self.assertRaises(TypeError):
+            x.value = "y"
         c_char.from_param(b"x")
+        self.assertRaises(TypeError, c_char.from_param, "x")
         (c_char * 3)(b"a", b"b", b"c")
+        self.assertRaises(TypeError, c_char * 3, "a", "b", "c")
 
     def test_c_wchar(self):
         x = c_wchar("x")
+        self.assertRaises(TypeError, c_wchar, b"x")
         x.value = "y"
+        with self.assertRaises(TypeError):
+            x.value = b"y"
         c_wchar.from_param("x")
+        self.assertRaises(TypeError, c_wchar.from_param, b"x")
         (c_wchar * 3)("a", "b", "c")
+        self.assertRaises(TypeError, c_wchar * 3, b"a", b"b", b"c")
 
     def test_c_char_p(self):
         c_char_p(b"foo bar")
+        self.assertRaises(TypeError, c_char_p, "foo bar")
 
     def test_c_wchar_p(self):
         c_wchar_p("foo bar")
+        self.assertRaises(TypeError, c_wchar_p, b"foo bar")
 
     def test_struct(self):
         class X(Structure):
             _fields_ = [("a", c_char * 3)]
 
         x = X(b"abc")
+        self.assertRaises(TypeError, X, "abc")
         self.assertEqual(x.a, b"abc")
         self.assertEqual(type(x.a), bytes)
 
@@ -35,6 +48,7 @@ class BytesTest(unittest.TestCase):
             _fields_ = [("a", c_wchar * 3)]
 
         x = X("abc")
+        self.assertRaises(TypeError, X, b"abc")
         self.assertEqual(x.a, "abc")
         self.assertEqual(type(x.a), str)
 
@@ -46,5 +60,6 @@ class BytesTest(unittest.TestCase):
 
         BSTR("abc")
 
+
 if __name__ == '__main__':
     unittest.main()
diff --git a/Lib/ctypes/test/test_structures.py b/Lib/ctypes/test/test_structures.py
index d1acc92b347..84d456c3cc3 100644
--- a/Lib/ctypes/test/test_structures.py
+++ b/Lib/ctypes/test/test_structures.py
@@ -322,7 +322,7 @@ class StructureTestCase(unittest.TestCase):
         self.assertEqual(cls, RuntimeError)
         self.assertEqual(msg,
                              "(Phone) <class 'TypeError'>: "
-                             "expected string, int found")
+                             "expected bytes, int found")
 
         cls, msg = self.get_except(Person, b"Someone", (b"a", b"b", b"c"))
         self.assertEqual(cls, RuntimeError)
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 01adbb5655a..fd00e5338cf 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -1080,7 +1080,7 @@ CharArray_set_raw(CDataObject *self, PyObject *value)
     ptr = view.buf;
     if (size > self->b_size) {
         PyErr_SetString(PyExc_ValueError,
-                        "string too long");
+                        "byte string too long");
         goto fail;
     }
 
@@ -1132,7 +1132,7 @@ CharArray_set_value(CDataObject *self, PyObject *value)
     size = PyBytes_GET_SIZE(value);
     if (size > self->b_size) {
         PyErr_SetString(PyExc_ValueError,
-                        "string too long");
+                        "byte string too long");
         Py_DECREF(value);
         return -1;
     }
@@ -1471,7 +1471,7 @@ c_wchar_p_from_param(PyObject *type, PyObject *value)
         Py_INCREF(Py_None);
         return Py_None;
     }
-    if (PyUnicode_Check(value) || PyBytes_Check(value)) {
+    if (PyUnicode_Check(value)) {
         PyCArgObject *parg;
         struct fielddesc *fd = _ctypes_get_fielddesc("Z");
 
@@ -1623,25 +1623,8 @@ c_void_p_from_param(PyObject *type, PyObject *value)
         return (PyObject *)parg;
     }
     /* XXX struni: remove later */
-/* string */
-    if (PyBytes_Check(value)) {
-        PyCArgObject *parg;
-        struct fielddesc *fd = _ctypes_get_fielddesc("z");
-
-        parg = PyCArgObject_new();
-        if (parg == NULL)
-            return NULL;
-        parg->pffi_type = &ffi_type_pointer;
-        parg->tag = 'z';
-        parg->obj = fd->setfunc(&parg->value, value, 0);
-        if (parg->obj == NULL) {
-            Py_DECREF(parg);
-            return NULL;
-        }
-        return (PyObject *)parg;
-    }
 /* bytes */
-    if (PyByteArray_Check(value)) {
+    if (PyBytes_Check(value)) {
         PyCArgObject *parg;
         struct fielddesc *fd = _ctypes_get_fielddesc("z");
 
@@ -3218,7 +3201,7 @@ _get_name(PyObject *obj, char **pname)
         return *pname ? 1 : 0;
     }
     PyErr_SetString(PyExc_TypeError,
-                    "function name must be string or integer");
+                    "function name must be string, bytes object or integer");
     return 0;
 }
 
diff --git a/Modules/_ctypes/cfield.c b/Modules/_ctypes/cfield.c
index 79d60f3728d..2078291731d 100644
--- a/Modules/_ctypes/cfield.c
+++ b/Modules/_ctypes/cfield.c
@@ -1160,7 +1160,7 @@ c_set(void *ptr, PyObject *value, Py_ssize_t size)
     }
   error:
     PyErr_Format(PyExc_TypeError,
-                 "one character string expected");
+                 "one character bytes, bytearray or integer expected");
     return NULL;
 }
 
@@ -1295,7 +1295,7 @@ s_set(void *ptr, PyObject *value, Py_ssize_t length)
         Py_INCREF(value);
     } else {
         PyErr_Format(PyExc_TypeError,
-                     "expected string, %s found",
+                     "expected bytes, %s found",
                      value->ob_type->tp_name);
         return NULL;
     }
@@ -1311,7 +1311,7 @@ s_set(void *ptr, PyObject *value, Py_ssize_t length)
         ++size;
     } else if (size > length) {
         PyErr_Format(PyExc_ValueError,
-                     "string too long (%zd, maximum length %zd)",
+                     "bytes too long (%zd, maximum length %zd)",
                      size, length);
         Py_DECREF(value);
         return NULL;