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 23:17:48 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 23:17:48 2013 +0800
@@ -239,19 +239,21 @@
         *target = '\0';
         if (src != Py_None) {
             Py_ssize_t len;
+            if (!PyUnicode_Check(src))
+                goto err;
             len = PyUnicode_GetLength(src);
-            if (len > 1) {
-                PyErr_Format(PyExc_TypeError,
-                    "\"%s\" must be an 1-character string",
-                    name);
-                return -1;
-            }
+            if (len > 1)
+                goto err;
             /* PyUnicode_READY() is called in PyUnicode_GetLength() */
             if (len > 0)
                 *target = PyUnicode_READ_CHAR(src, 0);
         }
     }
     return 0;
+err:
+    PyErr_Format(PyExc_TypeError,
+        "\"%s\" must be an 1-character string", name);
+    return -1;
 }
 
 static int