diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index b1a5110e2dcaa5efd9d3ad6158d920570b620da9..b901f06ca494459171a0b961bd11ec7ba0c36def 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1382,7 +1382,9 @@ def has_one(name, options = {})
# and +decrement_counter+. The counter cache is incremented when an object of this
# class is created and decremented when it's destroyed. This requires that a column
# named #{table_name}_count (such as +comments_count+ for a belonging Comment class)
- # is used on the associate class (such as a Post class). You can also specify a custom counter
+ # is used on the associate class (such as a Post class) - that is the migration for
+ # #{table_name}_count is created on the associate class (such that Post.comments_count will
+ # return the count cached, see note below). You can also specify a custom counter
# cache column by providing a column name instead of a +true+/+false+ value to this
# option (e.g., :counter_cache => :my_custom_counter.)
# Note: Specifying a counter cache will add it to that model's list of readonly attributes