I started to use biblatex not so long ago. Everything is working properly in general, however, I have had some trouble with the special character \'i, used in order to obtain the character "í".

It will render only under very specific conditions. For example, I have had no trouble when render it using the book entry type, but with the misc entry type there is almost every time a problem and here is where the specific conditions begin. Let's see the MWE first.





As you can see this MWE causes an error, a curious thing discovered is that if you make a brief modification in the references.bib file, the error is gone: instead of {\'a}{\'i} put {\'i}{\'a}.

A brief look at the output.bbl file can tell what is happening in the background: the input \'i is being interpreted as \'\i{}. This happens both in the misc and book entry types, the difference is that, for some reason, if the reference.bib (without the previous modification) is modified changing the entry type from misc to book, it will render without problem.


How can this be fixed? What should be the correct workaround?

Additional info

I am working in an online platform (namely Overleaf).

  • Please see Input encoding error after upgrading from Biber 1.9 to Biber 2.1 and related and linked questions.
    – moewe
    Apr 16, 2016 at 7:50
  • Seems as though \MakeSentenceCase has some problems with the characters ... (biblatex-ieee uses \MakeSentenceCase for @miscs, but not for @books). But maybe Biber's output routine needs tweaking.
    – moewe
    Apr 16, 2016 at 8:06
  • Do you know which version of biber Overleaf is using?
    – PLK
    Apr 16, 2016 at 8:24
  • @moewe Your comment reminds me another test I performed. The referencing style I have is IEEE, as you can see. The first character in the title is set to uppercase, and the rest of them are set to lowercase. Probably you noticed that when the \'i is at the beginning no uppercase alteration is performed. One more thing is that if you delete the \'a (leaving the \'i alone), the problem disappears but no character is rendered.
    – Hans
    Apr 16, 2016 at 8:40
  • 1
    @PLK I can reproduce the behaviour with current Biber 2.4. I guess that \MakeSentenceCase has some trouble with the characters from the .bbl (\'{a}\'\i{}).
    – moewe
    Apr 16, 2016 at 11:06

1 Answer 1


(You mentioned that you're working on Overleaf, so here's what you can do to get your Overleaf project to compile correctly.)

Method 1: Use XeLaTeX or LuaLaTeX

...which are able to handle UTF8 characters out of the box.

On Overleaf, you can set the engine to use by clicking on the Settings icon (the gear icon on the upper right of the editor, just next to your user name), and then selecting XeLaTeX or LuaLaTeX from the "LaTeX engine" drop list. Don't forget to click on "Save Project Settings".

Method 2: Tweak biber

If you need to use pdfLaTeX, you can tweak biber to use the --output-safechars option, as outlined in Input encoding error after upgrading from Biber 1.9 to Biber 2.1.

On Overleaf, you can do this by adding a latexmkrc file to your project, and then put the following line in it:

$biber = "biber --output-safechars %O %S";

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