/usr/include/CImg.h uses PATH_MAX, which is defined on unix but not on Hurd. The issue has a bit of history, https://www.gnu.org/software/hurd/hurd/porting/guidelines.html https://www.gnu.org/software/hurd/user/tlecarrour/porting_guide_for_dummies.html https://www.gnu.org/software/hurd/community/gsoc/project_ideas/maxpath.html http://insanecoding.blogspot.com/2007/11/pathmax-simply-isnt.html https://lists.debian.org/debian-hurd/2025/01/msg00013.html https://reviews.llvm.org/D53410 The simplest workaround is to just define it (e.g. to 1024 or 4096) in CImg.h if it's not already defined. It's currently affecting jkqtplotter, https://buildd.debian.org/status/fetch.php?pkg=jkqtplotter&arch=hurd-i386&ver=5.0.0%7Ebeta2%2Bgit20260626.e82cd41%2Bdfsg1-1&stamp=1782580500&raw=0