diff --git a/README.md b/README.md
index b63a246..0261be1 100644
--- a/README.md
+++ b/README.md
@@ -1,67 +1,67 @@
 # Self-Hosted Sentry nightly
 
 Official bootstrap for running your own [Sentry](https://sentry.io/) with [Docker](https://www.docker.com/).
 
 ## Requirements
 
 * Docker 19.03.6+
 * Compose 1.28.0+
 * 4 CPU Cores
 * 8 GB RAM
 * 20 GB Free Disk Space
 
 ## Setup
 
 ### Installation
 
 To get started with all the defaults, simply clone the repo and run `./install.sh` in your local check-out. Sentry uses Python 3 by default since December 4th, 2020 and Sentry 21.1.0 is the last version to support Python 2.
 
 During the install, a prompt will ask if you want to create a user account. If you require that the install not be blocked by the prompt, run `./install.sh --skip-user-prompt`.
 
 Thinking of not managing this yourself? Check out the [SaaS migration docs](https://docs.sentry.io/product/sentry-basics/migration/) or [contact us](https://sentry.io/from/self-hosted) for help.
 
 Please visit [our documentation](https://develop.sentry.dev/self-hosted/) for everything else.
 
 ### Customize DotEnv (.env) file
 
-Environment specific configurations can be done in the `.env.custom` file. It will be located in the root directory of the Sentry installation.
+Environment specific configurations can be done in the `.env.custom` file. It will be located in the root directory of the Sentry installation, and if it exists then `.env` will be ignored entirely.
 
 By default, there exists no `.env.custom` file. In this case, you can manually add this file by copying the `.env` file to a new `.env.custom` file and adjust your settings in the `.env.custom` file.
 
-Please keep in mind to check the `.env` file for changes, when you perform an upgrade of Sentry, so that you can adjust your `.env.custom` accordingly, if required.
+Please keep in mind to check the `.env` file for changes, when you perform an upgrade of Sentry, so that you can adjust your `.env.custom` accordingly, if required, as `.env` is ignored entirely if `.env.custom` is present.
 
 ### Enhance Sentry image
 
 To install plugins and their dependencies or make other modifications to the Sentry base image,
 copy `sentry/enhance-image.example.sh` to `sentry/enhance-image.sh` and add necessary steps there.
 For example, you can use `apt-get` to install dependencies and use `pip` to install plugins.
 
 After making modifications to `sentry/enhance-image.sh`, run `./install.sh` again to apply them.
 
 ## Tips & Tricks
 
 ### Event Retention
 
 Sentry comes with a cleanup cron job that prunes events older than `90 days` by default. If you want to change that, you can change the `SENTRY_EVENT_RETENTION_DAYS` environment variable in `.env` or simply override it in your environment. If you do not want the cleanup cron, you can remove the `sentry-cleanup` service from the `docker-compose.yml`file.
 
 ### Installing a specific SHA
 
 If you want to install a specific release of Sentry, use the tags/releases on this repo.
 
 We continuously push the Docker image for each commit made into [Sentry](https://github.com/getsentry/sentry), and other services such as [Snuba](https://github.com/getsentry/snuba) or [Symbolicator](https://github.com/getsentry/symbolicator) to [our Docker Hub](https://hub.docker.com/u/getsentry) and tag the latest version on master as `:nightly`. This is also usually what we have on sentry.io and what the install script uses. You can use a custom Sentry image, such as a modified version that you have built on your own, or simply a specific commit hash by setting the `SENTRY_IMAGE` environment variable to that image name before running `./install.sh`:
 
 ```shell
 SENTRY_IMAGE=getsentry/sentry:83b1380 ./install.sh
 ```
 
 Note that this may not work for all commit SHAs as this repository evolves with Sentry and its satellite projects. It is highly recommended to check out a version of this repository that is close to the timestamp of the Sentry commit you are installing.
 
 ### Using Linux
 
 If you are using Linux and you need to use `sudo` when running `./install.sh`, make sure to place the environment variable *after* `sudo`:
 
 ```shell
 sudo SENTRY_IMAGE=us.gcr.io/sentryio/sentry:83b1380 ./install.sh
 ```
 
 Where you replace `83b1380` with the sha you want to use.
diff --git a/install/_lib.sh b/install/_lib.sh
index f8a104b..3080c8d 100644
--- a/install/_lib.sh
+++ b/install/_lib.sh
@@ -1,54 +1,56 @@
 set -euo pipefail
 test "${DEBUG:-}" && set -x
 
 # Override any user-supplied umask that could cause problems, see #1222
 umask 002
 
 # Thanks to https://unix.stackexchange.com/a/145654/108960
 log_file="sentry_install_log-`date +'%Y-%m-%d_%H-%M-%S'`.txt"
 exec &> >(tee -a "$log_file")
 
 # Work from /install/ for install.sh, project root otherwise
 if [[ "$(basename $0)" = "install.sh"  ]]; then
   cd "$(dirname $0)/install/"
 else
   cd "$(dirname $0)"  # assume we're a test script or some such
 fi
 
-# Allow `.env` overrides using the `.env.custom` file
-if [[ -f "../.env.custom" ]]; then
-  _ENV="$(realpath ../.env.custom)"
+# Allow `.env` overrides using the `.env.custom` file.
+# We pass this to docker compose in a couple places.
+basedir="$( cd .. ; pwd -P )"  # realpath is missing on stock macOS
+if [[ -f "$basedir/.env.custom" ]]; then
+  _ENV="$basedir/.env.custom"
 else
-  _ENV="$(realpath ../.env)"
+  _ENV="$basedir/.env"
 fi
 
 # Read .env for default values with a tip o' the hat to https://stackoverflow.com/a/59831605/90297
 t=$(mktemp) && export -p > "$t" && set -a && . $_ENV && set +a && . "$t" && rm "$t" && unset t
 
 if [ "${GITHUB_ACTIONS:-}" = "true" ]; then
   _group="::group::"
   _endgroup="::endgroup::"
 else
   _group="▶ "
   _endgroup=""
 fi
 
 # A couple of the config files are referenced from other subscripts, so they
 # get vars, while multiple subscripts call ensure_file_from_example.
 function ensure_file_from_example {
   if [[ -f "$1" ]]; then
     echo "$1 already exists, skipped creation."
   else
     echo "Creating $1..."
     cp -n $(echo "$1" | sed 's/\.[^.]*$/.example&/') "$1"
     # sed from https://stackoverflow.com/a/25123013/90297
   fi
 }
 SENTRY_CONFIG_PY='../sentry/sentry.conf.py'
 SENTRY_CONFIG_YML='../sentry/config.yml'
 
 # Increase the default 10 second SIGTERM timeout
 # to ensure celery queues are properly drained
 # between upgrades as task signatures may change across
 # versions
 STOP_TIMEOUT=60 # seconds