Dear devs, The \adjustspacing register is described in the LuaTeX manual as follows: When \adjustspacing has value 2, hz optimization will be applied to glyphs and kerns. When the value is 3, only glyphs will be treated. A value smaller than 2 disables this feature. However, setting \adjustspacing=1 will only disable shrink but not stretch. Please find a minimal example example, where I have used exaggerated values for shrink and stretch to emphasize the issue. It can be reproduced with both mtxrun --script plain and luatex with luaotfload.sty. I have already checked linebreak.c but add_to_widths looks innocuous and properly checks the adjust_spacing parameter. Cheers, Henri --- %\input luaotfload.sty \directlua{ fonts.expansions.setups.default.stretch = 2000 fonts.expansions.setups.default.shrink = 2000 } \adjustspacing=1 \font\1="file:lmroman10-regular.otf:expansion=default" \hsize=5em \1 \input lorem \bye