“texlive-latex-base” provides that file. We disable a whole bunch of formats that we cannot build that early in the process, and then we run fmtutil-sys on the patched file. The cause for trouble lies in texlive-kpathsea, which provides share/texmf-dist/web2c/fmtutil.cnf . That file states how to build the various fmt files. The file in the earlier version of Tex Live contains this line for the lualatex format: lualatex luatex language.dat,language.dat.lua lualatex.ini the new file (on core-updates-frozen) says this: lualatex luahbtex language.dat,language.dat.lua lualatex.ini i.e. it will try to build the lualatex fmt file with luahbtex instead of luatex. I suppose at this point in the build we don’t actually have a working luahbtex, so fmtutil-sys doesn’t generate the correct lualatex.fmt. I’m not sure how to fix this, but I guess we can avoid a world rebuild by adding an extra package that installs a working lualatex.fmt file. -- Ricardo