Hi, on line 226 the wrong parameter is passed to \setupcurrentmathfence. \tolerant\protected\def\math_fenced_fenced[#1]#*[#2]%   {\advance\c_math_fenced_nesting\plusone    \begingroup    \edef\currentmathfence{#1}% -  \ifparameter#2\or\setupcurrentmathfence[#1]\fi +  \ifparameter#2\or\setupcurrentmathfence[#2]\fi    \math_fenced_fenced_common    \edef\p_size{\mathfenceparameter\c!size}%    \ifempty\p_size      \expandafter\math_fenced_fenced_indeed_adapt    \else      \expandafter\math_fenced_fenced_indeed_fixed    \fi} Wolfgang