diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index 6f6e96f..7c7b96e 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -1103,6 +1103,9 @@
         self.assertRaises(ValueError, u"{:}".format)
         self.assertRaises(ValueError, u"{:s}".format)
         self.assertRaises(ValueError, u"{}".format)
+        big = "23098475029384702983476098230754973209482573"
+        self.assertRaises(ValueError, ("{" + big + "}").format)
+        self.assertRaises(ValueError, ("{[" + big + "]}").format, [0])
 
         # issue 6089
         self.assertRaises(ValueError, u"{0[0]x}".format, [None])