diff --git a/config/environments/production.rb b/config/environments/production.rb
index 505d507d..653cd817 100644
--- a/config/environments/production.rb
+++ b/config/environments/production.rb
@@ -62,7 +62,7 @@
   # Use a real queuing backend for Active Job
   config.active_job.queue_adapter = :resque
 
-  config.action_mailer.default_url_options = { host: 'sul-preassembly-prod.stanford.edu' } # needed by url_for() in mail templates
+  config.action_mailer.default_url_options = { host: 'sul-preassembly-prod.stanford.edu', protocol: 'https' } # needed by url_for() in mail templates
   config.action_mailer.perform_caching = false
 
   # Ignore bad email addresses and do not raise email delivery errors.