Work on a temporary file, not the input file.
diff --git a/Doc/tools/fix.el b/Doc/tools/fix.el
index 994b509..f41fb59 100644
--- a/Doc/tools/fix.el
+++ b/Doc/tools/fix.el
@@ -1,5 +1,5 @@
 ; load the new texinfo package (2.xx) if not installed by default
 ; (setq load-path (cons "/ufs/guido/lib/emacs/texinfo-2.14" load-path))
-(find-file "lib1.texi")
+(find-file "temp.texi")
 (texinfo-all-menus-update t)
 (texinfo-all-menus-update t)