diff --git a/README.md b/README.md
index 247bfba..902b898 100644
--- a/README.md
+++ b/README.md
@@ -140,6 +140,11 @@ The build runs for hours and needs disk. On the Gitea runner host:
   3h) must match, otherwise Gitea kills the job at 3h regardless of the runner.
 - Roughly 40–60 GB of free disk for the build tree, the bundled R and the
   staged install.
+- **Swap.** `rstanarm` (required by `jaspMixedModels`) and `OpenMx` generate
+  translation units where a single `cc1plus` wants 4–8 GB. Without swap an
+  over-commit is an instant OOM kill, which surfaces only as a module that never
+  builds. 16 GB RAM plus 8 GB swap, with R packages compiled at `R_JOBS=1`, is
+  what this build was verified against.
 
 ## Running it by hand