diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index 6e4f048..75637f8 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -687,6 +687,9 @@
         self.assertRaises(IndexError, "{:}".format)
         self.assertRaises(IndexError, "{:s}".format)
         self.assertRaises(IndexError, "{}".format)
+        big = "23098475029384702983476098230754973209482573"
+        self.assertRaises(ValueError, ("{" + big + "}").format)
+        self.assertRaises(ValueError, ("{[" + big + "]}").format, [0])
 
         # issue 6089
         self.assertRaises(ValueError, "{0[0]x}".format, [None])