Some days ago an l3kernel etc update was announced. It mentioned: - Move experimental l3luatex code out of l3kernel: this requires more work before inclusion in the 'stable' release bundle But where has the code been moved too? Unicode-math actually did use some of the code and now breaks due to the missing \lua_now_x:n: \documentclass{article} \usepackage{amsmath} \usepackage{unicode-math} \begin{document} blub \end{document} ! Undefined control sequence. \__lltxmath_set_mathchar:NN ...def #1\lua_now_x:n {lualatex.math.print_class... (Adding \usepackage{expl3} \ExplSyntaxOn \let\lua_now_x:n\directlua \ExplSyntaxOff before unicode-math avoids the error) -- Ulrike Fischer http://www.troubleshooting-tex.de/