correctly overflow when indexes are too large
diff --git a/Misc/NEWS b/Misc/NEWS
index dfdda16..4424228 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Core and Builtins
 -----------------
 
+- In the unicode/str.format(), raise a ValueError when either indexes to
+  arguments are too large.
+
 Library
 -------