diff --git a/lib/sidekiq/middleware/server/active_record.rb b/lib/sidekiq/middleware/server/active_record.rb
index f6e7ca365..64c16b0da 100644
--- a/lib/sidekiq/middleware/server/active_record.rb
+++ b/lib/sidekiq/middleware/server/active_record.rb
@@ -7,7 +7,7 @@ class ActiveRecord
         def initialize
           # With Rails 5+ we must use the Reloader **always**.
           # The reloader handles code loading and db connection management.
-          if defined?(::Rails) && ::Rails::VERSION::MAJOR >= 5
+          if defined?(::Rails) && defined?(::Rails::VERSION) && ::Rails::VERSION::MAJOR >= 5
             raise ArgumentError, "Rails 5 no longer needs or uses the ActiveRecord middleware."
           end
         end