I have the following entry in my bib-file which contains the accented character \u\i:

@article {Gur1966SpacesUniversalPlacement,
    author = {Gurari{\u{\i}}, V. I.},
     title = {Spaces of universal placement, isotropic spaces and a problem of {M}azur on rotations of {B}anach spaces},
   journal = {Sibirsk. Mat. \v{Z}.},
    volume = {7},
      year = {1966},
     pages = {1002--1013},

When I use BibTeX the correct entry is generated. Using Biber results in the following error message:

Undefined control sequence.

It seems that the backslash in \u\i is removed. Is it possible to prevent Biber from doing this? Or more general, what is the proper way of using accented characters with Biber?

  • Just use the correct unicode character.
    – Johannes_B
    Apr 12, 2016 at 8:37
  • By the way, in an up to date version of biber, this should be resolved.
    – Johannes_B
    Apr 12, 2016 at 8:43
  • @Johannes_B: I tried to use the unicode character "ĭ" but then I ran into troubles with fontenc. It seems that ĭ is not in T1.
    – Christian
    Apr 12, 2016 at 8:54
  • ĭ works fine for me with \usepackage[T1]{fontenc}. Perhaps your inputenc setting and/or the encoding of the bib is faulty. Apr 12, 2016 at 9:12
  • 1
    @egreg That \u{\i} doesn't work is not really a surprise, but the direct input ĭ should work if the (input) encodings are correct and correctly declared. Apr 12, 2016 at 9:27

1 Answer 1


There's a strange combination of factors that should be solved by different people.

  1. There's no predefined combination \u{i} in t1enc.def, so ĭ should be typed in as \u{\i}

  2. Biber transforms \u{i} into U+012D LATIN SMALL LETTER I WITH BREVE

  3. Biber transforms \u{\i} into U+0131 LATIN SMALL LETTER DOTLESS I U+0306 COMBINING BREVE

So the legal LaTeX input Gurari{\u{\i}} becomes a combination that makes sense to Unicode engines (XeTeX and LuaTeX) because of their normalization rules, but is pretty useless with pdflatex.

Solution: in the author field either type in




(the latter requires you load \usepackage[utf8]{inputenc}

  • the problem goes beyond that - the second character (U+0131) does not have coverage on some very standard fonts, like for example, Times New Roman, so the following code, even under xelatex produces a square in the place of the accent: \documentclass{report} \usepackage[utf8]{inputenc} \RequirePackage{fontspec} \setmainfont{Times New Roman} \begin{document} Oleı̆nik. \end{document}
    – Paulo Ney
    Apr 18, 2018 at 21:08
  • @PauloNey If a font doesn't have the necessary glyphs, it's not the fault of the maintainers of Biblatex. Please make a new question with the details.
    – egreg
    Apr 18, 2018 at 21:18
  • @egreg You are my hero of the day! (+1 of course). Aug 14, 2019 at 16:38

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