With biber 2.6 comes a unnecassary warning:

 [15251] Utils.pm:164> WARN - month field 'Apr' in entry 'GSP+08' is not an integer - this will probably not sort properly.

Is the three letter month code no longer supported? the warning clatters the log.

  • What happens with lower case 'apr'? – PLK Sep 18 '16 at 13:57
  • 3
    It's also not recommended to use year/month fields - the date field has many more features and year/month are considered legacy in biber even though they are still supported. – PLK Sep 18 '16 at 13:59
  • Case should not matter - can you give a MWE? – PLK Sep 18 '16 at 14:21
  • you will find a minimal example together with the bib-file here: b-kleine.com/technical/tex_20160918. Running latexmk on the file and later again biber shows the warning. Regards – Bernhard Kleine Sep 18 '16 at 18:36
  • 2
    This is only a single bibtex entry. I have however 800+ citations in my document and never before this warning. Therefore I would like to know how to get rid of the warning. It is my understanding that three-letter-code for the month field is still valid. Therefore there should be any warning. – Bernhard Kleine Sep 18 '16 at 19:07

Such month abbreviations are BibTeX macros and if you protect them in braces, they are not parsed as macros but as literal strings. You need, in your example:


and not

MONTH = {Dec}

For information, biber allows one to turn off such macros with the --nostdmacros option.


Month is an integer field, that means January is {1}, February {2} etc.

  • 2
    Please see tex.stackexchange.com/a/386058/36296 Without braces the abbreviated month names are ok – samcarter_is_at_topanswers.xyz Jan 9 '19 at 14:52
  • 1
    That is true. And one could even give the integer without braces (because BIbTeX allows that). But with most .bst files and with biblatex it is also valid to use the three-letter abbreviations, but there it is crucial that they are used without braces. – moewe Jan 9 '19 at 15:13
  • I should mention though that I believe, correct as this info is, that it does not quite answer the question which specifically asks about whether or not three-letter abbreviations are legal (with or without braces). – moewe Jan 9 '19 at 15:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.