diff -r 8345fb616cbd Lib/test/test_csv.py
--- a/Lib/test/test_csv.py	Sun Aug 25 14:57:38 2013 +0200
+++ b/Lib/test/test_csv.py	Sun Aug 25 23:08:30 2013 +0800
@@ -791,6 +791,15 @@
         mydialect.lineterminator = 4
         self.assertRaises(csv.Error, mydialect)
 
+    def test_invaliddelimiter(self):
+        class mydialect(csv.Dialect):
+            delimiter = b","
+
+        with self.assertRaises(csv.Error) as cm:
+            mydialect()
+        self.assertEqual(str(cm.exception),
+                         '"delimiter" must be an 1-character string')
+
 
 class TestSniffer(unittest.TestCase):
     sample1 = """\
diff -r 8345fb616cbd Modules/_csv.c
--- a/Modules/_csv.c	Sun Aug 25 14:57:38 2013 +0200
+++ b/Modules/_csv.c	Sun Aug 25 23:08:30 2013 +0800
@@ -240,7 +240,8 @@
         if (src != Py_None) {
             Py_ssize_t len;
             len = PyUnicode_GetLength(src);
-            if (len > 1) {
+            /* -1 length mean src is not str */
+            if (len == -1 || len > 1) {
                 PyErr_Format(PyExc_TypeError,
                     "\"%s\" must be an 1-character string",
                     name);