diff --git a/docs/Formula-Cookbook.md b/docs/Formula-Cookbook.md
index 68283dd9ed..71cc55435e 100644
--- a/docs/Formula-Cookbook.md
+++ b/docs/Formula-Cookbook.md
@@ -1175,6 +1175,8 @@ brew search --fink foo
 
 `superenv` is our "super environment" that isolates builds by removing `/usr/local/bin` and all user `PATH`s that are not essential for the build. It does this because user `PATH`s are often full of stuff that breaks builds. `superenv` also removes bad flags from the commands passed to `clang`/`gcc` and injects others (for example all [`keg_only`](https://rubydoc.brew.sh/Formula#keg_only-class_method) dependencies are added to the `-I` and `-L` flags).
 
+If in your local Homebrew build of your new formula, you see `Operation not permitted` errors, this will be because your new formula tried to write to the disk outside of your sandbox area. This is enforced on MacOS by `sandbox-exec`.
+
 ### Fortran
 
 Some software requires a Fortran compiler. This can be declared by adding `depends_on "gcc"` to a formula.