# Caron accent in the bibliography causes a microtype error

I'm getting the microtype-related error ! Argument of \MT@res@a has an extra }. when trying to compile a BibLaTeX bibliography that contains a caracter with a caron accent (\v{a}, i.e., ǎ).

Here's a minimal example (file microtype.tex):

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{microtype}
\usepackage{biblatex}
\usepackage{filecontents}
\begin{filecontents}{microtype.bib}
@Article{         ref,
author        = {Name, \v{a}},
}
\end{filecontents}
\bibliography{microtype.bib}
\begin{document}
\cite{ref}
\printbibliography
\end{document}


When compiling this file as follows:

pdflatex microtype
biber microtype
pdflatex microtype


I get the following error:

(/usr/share/texlive/texmf-dist/tex/latex/biblatex/lbx/english.lbx)
(./microtype.aux) (/usr/share/texlive/texmf-dist/tex/latex/microtype/mt-cmr.cfg
) (./microtype.bbl)
! Argument of \MT@res@a has an extra }.
<inserted text>
\par
l.16 \end
{document}
?


Any ideas about how to fix this problem? Thanks a lot in advance!

The problem still occurs if I run biber --output-safechars microtype. Oddly enough, the problem does not happen with other accents, i.e., the document compiles fine with \'{a} instead of \v{a}. The error I'm having was also mentioned in another question but there are no specific insights there.

The error seems to be similar to the one described in Biber 2.4, microtype, and special characters

The workaround seems to consist in fixing the definition of \ifempty:

\begin{filecontents}{\jobname.bib}
@Article{ref,
author = {Name, \v{a}},
}
\end{filecontents}

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{microtype}
\usepackage{biblatex}

% fix the bad definition of \ifempty
\makeatletter
\def\ifempty#1{%
\protected@edef\z{#1}\expandafter\ifblank\expandafter{\z}%
}
\makeatother

\begin{document}

\cite{ref}

\printbibliography

\end{document}

• I had missed the question you were linking to. Indeed, this seems to fix the bug. Thanks a lot for your help! – a3nm May 9 '16 at 12:38
• This is fixed in version 3.4 which us in beta. – PLK May 9 '16 at 14:58