diff --git a/config/initializers/deprecations.rb b/config/initializers/deprecations.rb
index e0ad54d8c3..f9f3745d6a 100644
--- a/config/initializers/deprecations.rb
+++ b/config/initializers/deprecations.rb
@@ -3,14 +3,16 @@
 if ENV['REDIS_NAMESPACE']
   es_configured = ENV['ES_ENABLED'] == 'true' || ENV.fetch('ES_HOST', 'localhost') != 'localhost' || ENV.fetch('ES_PORT', '9200') != '9200' || ENV.fetch('ES_PASS', 'password') != 'password'
 
-  warn <<~MESSAGE
-    WARNING: the REDIS_NAMESPACE environment variable is deprecated and will be removed in Mastodon 4.4.0.
+  message = <<~MESSAGE
+    ERROR: the REDIS_NAMESPACE environment variable is no longer supported, and a migration is required.
 
     Please see documentation at https://github.com/mastodon/redis_namespace_migration
   MESSAGE
 
-  warn <<~MESSAGE if es_configured && !ENV['ES_PREFIX']
+  message += <<~MESSAGE if es_configured && !ENV['ES_PREFIX']
 
     In addition, as REDIS_NAMESPACE is being used as a prefix for Elasticsearch, please do not forget to set ES_PREFIX to "#{ENV.fetch('REDIS_NAMESPACE')}".
   MESSAGE
+
+  abort message
 end