diff --git a/tornado/test/web_test.py b/tornado/test/web_test.py
index c475520b..2f595af6 100644
--- a/tornado/test/web_test.py
+++ b/tornado/test/web_test.py
@@ -1954,6 +1954,20 @@ class XSRFTest(SimpleHandlerTestCase):
                 body=urllib_parse.urlencode(dict(_xsrf=self.xsrf_token)))
         self.assertEqual(response.code, 403)
 
+    def test_xsrf_success_short_token(self):
+        with ExpectLog(gen_log, ".*XSRF cookie does not match POST"):
+            response = self.fetch(
+                "/", method="POST",
+                body=urllib_parse.urlencode(dict(_xsrf='deadbeef')))
+        self.assertEqual(response.code, 403)
+
+    def test_xsrf_success_non_hex_token(self):
+        with ExpectLog(gen_log, ".*XSRF cookie is not a hexadecimal"):
+            response = self.fetch(
+                "/", method="POST",
+                body=urllib_parse.urlencode(dict(_xsrf='xoxo')))
+        self.assertEqual(response.code, 400)
+
     def test_xsrf_fail_cookie_no_body(self):
         with ExpectLog(gen_log, ".*'_xsrf' argument missing"):
             response = self.fetch(
diff --git a/tornado/web.py b/tornado/web.py
index 9fe2f77b..7147c17e 100644
--- a/tornado/web.py
+++ b/tornado/web.py
@@ -1140,14 +1140,15 @@ class RequestHandler(object):
             else:
                 # Treat unknown versions as not present instead of failing.
                 return None, None, None
-        elif len(cookie) == 32:
+        else:
             version = 1
-            token = binascii.a2b_hex(utf8(cookie))
+            try:
+                token = binascii.a2b_hex(utf8(cookie))
+            except TypeError:
+                raise HTTPError(400, "XSRF cookie is not a hexadecimal")
             # We don't have a usable timestamp in older versions.
             timestamp = int(time.time())
             return (version, token, timestamp)
-        else:
-            return None, None, None
 
     def check_xsrf_cookie(self):
         """Verifies that the ``_xsrf`` cookie matches the ``_xsrf`` argument.