# Why does biber say a checked-valid ISBN is invalid?

I get the following warning:

WARN - ISBN '0-13-603313-X, 978-0-13-603313-4' in entry 'sheldon' is invalid - run biber with '--validate_datamodel' for details.


But checking these ISBN against this and against this, it seems to be quite valid. What's up?

• Welcome to TeX.SX! Please help us (and also you) and add a minimal working example with bibliography (MWEB), that illustrates your problem. Reproducing the problem and finding out what the issue is will be much easier when we see compilable code, starting with \documentclass and ending with \end{document}. – Bobyandbob May 23 '18 at 13:53

## 1 Answer

There can only be one ISBN in the isbn field.

In

WARN - ISBN '0-13-603313-X, 978-0-13-603313-4' in entry 'sheldon' is invalid - run biber with '--validate_datamodel' for details.


it looks awfully like you have two ISBNs in the isbn field as in

isbn = {0-13-603313-X, 978-0-13-603313-4},


Throw away one of the two ISBNs and Biber will stop complaining

isbn = {978-0-13-603313-4},


The same holds for the url and doi field. Here Biber will not complain, but the output will be mangled, especially when hyperref is loaded.

• How applicable and possible would it be to assign more than one ISBN to a reference, either in the field isbn or by applying isbn multiple times? – naphaneal May 23 '18 at 16:43
• @naphaneal You can't use a field multiple times. So that is out. And as I say, multiple ISBNs in the isbn fields are not intended and will cause a warning (they will probably print OK, so if you want to ignore the warning, fine). If you absolutely need a second ISBN, you need to use a new field: tex.stackexchange.com/q/103671/35864 – moewe May 23 '18 at 17:28
• @naphaneal I fail to see how one would ever need several ISBNs. Pick ISBN-10 or ISBN-13 as it appears on the title page, if both are present prefer ISBN-13. If a book has a online and print ISBN use the one of the edition you used. – moewe May 23 '18 at 17:29
• @moewe Hardback and paperback publications may have differing ISBNs even though the contents are the same. – Peter Wilson May 23 '18 at 18:21
• @PeterWilson Fair enough. Still, I think normally it should be enough to just cite the ISBN of the version that you actually used. I can see that it might make sense to give several ISBNs for CVs or reading lists. – moewe May 23 '18 at 19:52