diff -r a1119cf551e8 -r fa9c38891cf2 src/Pure/Syntax/lexicon.ML
--- a/src/Pure/Syntax/lexicon.ML	Tue Aug 13 16:25:47 2013 +0200
+++ b/src/Pure/Syntax/lexicon.ML	Tue Aug 13 17:26:22 2013 +0200
@@ -295,7 +295,8 @@
     fun idxname cs ds = (implode (rev cs), nat 0 ds);
     fun chop_idx [] ds = idxname [] ds
       | chop_idx (cs as (_ :: "\\<^sub>" :: _)) ds = idxname cs ds
-      | chop_idx (cs as (_ :: "\\<^isub>" :: _)) ds = idxname cs ds
+      | chop_idx (cs as (_ :: "\\<^isub>" :: _)) ds = idxname cs ds  (*legacy*)
+      | chop_idx (cs as (_ :: "\\<^isup>" :: _)) ds = idxname cs ds  (*legacy*)
       | chop_idx (c :: cs) ds =
           if Symbol.is_digit c then chop_idx cs (c :: ds)
           else idxname (c :: cs) ds;