diff --git a/activesupport/lib/active_support/log_subscriber.rb b/activesupport/lib/active_support/log_subscriber.rb
index db991c7a32..8b9dd1fffe 100644
--- a/activesupport/lib/active_support/log_subscriber.rb
+++ b/activesupport/lib/active_support/log_subscriber.rb
@@ -29,6 +29,9 @@ module ActiveSupport
   # subscriber, the line above should be called after your
   # <tt>ActiveRecord::LogSubscriber</tt> definition.
   #
+  # A logger also needs to be set with <tt>ActiveRecord::LogSubscriber.logger=</tt>.
+  # This is assigned automatically in a Rails environment.
+  #
   # After configured, whenever a <tt>"sql.active_record"</tt> notification is published,
   # it will properly dispatch the event
   # (<tt>ActiveSupport::Notifications::Event</tt>) to the sql method.