diff --git a/README.md b/README.md
index 11d4269..2f71543 100644
--- a/README.md
+++ b/README.md
@@ -9,9 +9,11 @@ crafter-build ships as a Flatpak that carries its own clang, lld, libc++ and WAS
 ```bash
 flatpak remote-add --if-not-exists catcrafts https://flatpak.catcrafts.net/catcrafts.flatpakrepo
 flatpak install catcrafts net.catcrafts.CrafterBuild
-alias crafter-build='flatpak run net.catcrafts.CrafterBuild'
+alias crafter-build='flatpak run --die-with-parent net.catcrafts.CrafterBuild'
 ```
 
+`--die-with-parent` ends the sandbox with the `flatpak run` that started it. Without the flag, killing only the `flatpak run` process leaves the sandbox running: a build carries on writing into `bin/` and `build/`, and a program started with `-r` keeps running. With it, bubblewrap kills everything in the sandbox with SIGKILL when the `flatpak run` process dies or when that process's parent does. For `crafter-build …` or `crafter-build … &` typed at a bash or zsh prompt, that parent is the shell, so the sandbox ends with the shell, even after a `disown`. Ctrl-C reaches the program either way.
+
 Pre-release builds of `master` are the `beta` branch (`flatpak install catcrafts net.catcrafts.CrafterBuild//beta`), and every release also attaches a single-file bundle on the Forgejo releases page (`flatpak install --user crafter-build-<version>.flatpak`). The sandbox sees the whole host filesystem, so projects can live anywhere. Binaries built for the host link the bundled `libc++.so.1` through an rpath into the Flatpak: they run inside it (`-r`, the test runner), and are not meant to be copied out onto the host.
 
 ## Writing a project.cpp