MRuby 3.4.0 does not build on Debian+ARM (including RaspberryPi OS) due to a failing unit test in mruby-bigint. This was fixed in master in commit d7edd3dbc (Hendrik, Sun Aug 10 09:21:38 2025). It's a simple one-line change.

I would like to suggest that this change be cherry-picked onto the "stable" branch, since it fixes a significant issue on a major platform and is highly unlikely to introduce any kind of regression.