diff --git a/lib/mastodon/redis_configuration.rb b/lib/mastodon/redis_configuration.rb
index 3d739a2ac6..e4fa6e52ba 100644
--- a/lib/mastodon/redis_configuration.rb
+++ b/lib/mastodon/redis_configuration.rb
@@ -7,6 +7,13 @@ class Mastodon::RedisConfiguration
     db: 0,
   }.freeze
 
+  def reset!
+    @base = nil
+    @sidekiq = nil
+    @cache = nil
+    @namespace = nil
+  end
+
   def base
     @base ||= setup_config(prefix: nil, defaults: DEFAULTS)
               .merge(namespace: base_namespace)
diff --git a/lib/tasks/mastodon.rake b/lib/tasks/mastodon.rake
index 2822f2eeb1..a159a22264 100644
--- a/lib/tasks/mastodon.rake
+++ b/lib/tasks/mastodon.rake
@@ -8,14 +8,6 @@ namespace :mastodon do
     prompt = TTY::Prompt.new
     env    = {}
 
-    # When the application code gets loaded, it runs `lib/mastodon/redis_configuration.rb`.
-    # This happens before application environment configuration and sets REDIS_URL etc.
-    # These variables are then used even when REDIS_HOST etc. are changed, so clear them
-    # out so they don't interfere with our new configuration.
-    ENV.delete('REDIS_URL')
-    ENV.delete('CACHE_REDIS_URL')
-    ENV.delete('SIDEKIQ_REDIS_URL')
-
     begin
       errors = false
 
@@ -533,6 +525,11 @@ namespace :mastodon do
             ENV[key] = value.to_s
           end
 
+          # Redis configuration happens very early when the application code is loaded.
+          # This happens before the `mastodon:setup` task runs, so we have to refresh it with
+          # the new environment variable values.
+          REDIS_CONFIGURATION.reset!
+
           require_relative '../../config/environment'
           disable_log_stdout!