diff --git a/config/env.example b/config/env.example
index 9a3fc6d54..1a931103d 100644
--- a/config/env.example
+++ b/config/env.example
@@ -28,8 +28,16 @@ BASIC_AUTH_ENABLED="disabled"
 BASIC_AUTH_USERNAME=""
 BASIC_AUTH_PASSWORD=""
 
-# Object Storage for attachments
-FOG_ENABLED="disabled"
+# ActiveStorage service to use for attached files.
+# Possible values:
+# - "local": store files on the local filesystem
+# - "amazon": store files remotely on an S3 storage service
+# - "openstack": store files remotely on an OpenStack storage service
+#
+# (See config/storage.yml for the configuration of each service.)
+STORAGE_TYPE="local"
+
+# Configuration for the OpenStack storage service (if enabled)
 FOG_OPENSTACK_API_KEY=""
 FOG_OPENSTACK_USERNAME=""
 FOG_OPENSTACK_URL=""
diff --git a/config/environments/development.rb b/config/environments/development.rb
index ca4b53b87..6cd35bccc 100644
--- a/config/environments/development.rb
+++ b/config/environments/development.rb
@@ -40,7 +40,7 @@ Rails.application.configure do
   config.action_mailer.raise_delivery_errors = false
 
   # Store uploaded files on the local file system (see config/storage.yml for options).
-  config.active_storage.service = ENV['FOG_ENABLED'] == 'enabled' ? :openstack : :local
+  config.active_storage.service = ENV.fetch("STORAGE_TYPE").to_sym
 
   # Print deprecation notices to the Rails logger.
   config.active_support.deprecation = :log
diff --git a/config/environments/production.rb b/config/environments/production.rb
index 9c541639d..3a23d77fd 100644
--- a/config/environments/production.rb
+++ b/config/environments/production.rb
@@ -107,7 +107,7 @@ Rails.application.configure do
   # the I18n.default_locale when a translation cannot be found).
   config.i18n.fallbacks = true
 
-  config.active_storage.service = :openstack
+  config.active_storage.service = ENV.fetch("STORAGE_TYPE").to_sym
 
   # Send deprecation notices to registered listeners.
   config.active_support.deprecation = :notify