diff --git a/.rubocop.yml b/.rubocop.yml
index f567ec525..a4f10b1dd 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -410,6 +410,9 @@ Style/PercentLiteralDelimiters:
 Style/Proc:
   Enabled: true
 
+Style/RedundantFileExtensionInRequire:
+  Enabled: true
+
 Style/RedundantFreeze:
   Enabled: true
 
diff --git a/config/application.rb b/config/application.rb
index 935dffa93..e151e7cbd 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -129,4 +129,4 @@ class Rails::Engine
   end
 end
 
-require "./config/application_custom.rb"
+require "./config/application_custom"