diff --git a/ci/README.md b/ci/README.md
index a7291284b33..91a3cee30ad 100644
--- a/ci/README.md
+++ b/ci/README.md
@@ -28,8 +28,10 @@ the CI locally you may need to reduce that entropy by running:
 sudo sysctl -w vm.mmap_rnd_bits=28
 ```
 
-It is recommended to run the ci system in a clean env. To run the test stage
-with a specific configuration,
+It is recommended to run the CI system in a clean environment. The `env -i`
+command below ensures that *only* specified environment variables are propagated
+into the local CI.
+To run the test stage with a specific configuration:
 
 ```
 env -i HOME="$HOME" PATH="$PATH" USER="$USER" bash -c 'FILE_ENV="./ci/test/00_setup_env_arm.sh" ./ci/test_run_all.sh'