diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index a3c084306b7e..ed10ed79a476 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -32,6 +32,8 @@ def _test_arg_valid(self, ctor, arg):
         self.assertRaises(TypeError, ctor, arg, quoting=None)
         self.assertRaises(TypeError, ctor, arg, 
                           quoting=csv.QUOTE_ALL, quotechar='')
+        self.assertRaises(TypeError, ctor, arg, 
+                          quoting=csv.QUOTE_ALL, quotechar=None)
 
     def test_reader_arg_valid(self):
         self._test_arg_valid(csv.reader, [])
diff --git a/Modules/_csv.c b/Modules/_csv.c
index 30b7eca40901..c592933cb45e 100644
--- a/Modules/_csv.c
+++ b/Modules/_csv.c
@@ -401,7 +401,7 @@ dialect_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
                 PyErr_SetString(PyExc_TypeError, "delimiter must be set");
 		goto err;
 	}
-	if (quotechar == Py_None && self->quoting != QUOTE_NONE)
+	if (quotechar == Py_None && quoting == NULL)
 		self->quoting = QUOTE_NONE;
 	if (self->quoting != QUOTE_NONE && self->quotechar == 0) {
                 PyErr_SetString(PyExc_TypeError,