diff -r d489394a73de Lib/test/test_csv.py
--- a/Lib/test/test_csv.py	Tue Dec 17 15:12:46 2013 +0200
+++ b/Lib/test/test_csv.py	Thu Dec 19 11:05:16 2013 +0100
@@ -803,6 +803,20 @@ class TestDialectValidity(unittest.TestC
         mydialect.lineterminator = 4
         self.assertRaises(csv.Error, mydialect)
 
+    def test_invalid_chars(self):
+        def create_invalid(field_name, value):
+            class mydialect(csv.Dialect):
+                pass
+            setattr(mydialect, field_name, value)
+            d = mydialect()
+
+        for field_name in ("delimiter", "escapechar", "quotechar"):
+            with self.subTest(field_name=field_name):
+                self.assertRaises(csv.Error, create_invalid, field_name, "")
+                self.assertRaises(csv.Error, create_invalid, field_name, "abc")
+                self.assertRaises(csv.Error, create_invalid, field_name, b'x')
+                self.assertRaises(csv.Error, create_invalid, field_name, 5)
+
 
 class TestSniffer(unittest.TestCase):
     sample1 = """\
diff -r d489394a73de Modules/_csv.c
--- a/Modules/_csv.c	Tue Dec 17 15:12:46 2013 +0200
+++ b/Modules/_csv.c	Thu Dec 19 11:05:16 2013 +0100
@@ -240,15 +240,14 @@ static int
         if (src != Py_None) {
             Py_ssize_t len;
             len = PyUnicode_GetLength(src);
-            if (len > 1) {
+            if (len != 1) {
                 PyErr_Format(PyExc_TypeError,
                     "\"%s\" must be an 1-character string",
                     name);
                 return -1;
             }
             /* PyUnicode_READY() is called in PyUnicode_GetLength() */
-            if (len > 0)
-                *target = PyUnicode_READ_CHAR(src, 0);
+            *target = PyUnicode_READ_CHAR(src, 0);
         }
     }
     return 0;