diff --git a/activerecord/lib/active_record/associations/preloader/through_association.rb b/activerecord/lib/active_record/associations/preloader/through_association.rb
index 874b3fbe85..b469a9ca10 100644
--- a/activerecord/lib/active_record/associations/preloader/through_association.rb
+++ b/activerecord/lib/active_record/associations/preloader/through_association.rb
@@ -86,9 +86,14 @@ module ActiveRecord
             if options[:source_type]
               scope.where! reflection.foreign_type => options[:source_type]
             elsif !reflection_scope.where_clause.empty?
-              scope.includes_values = Array(values[:includes] || options[:source])
               scope.where_clause = reflection_scope.where_clause
 
+              if includes = values[:includes]
+                scope.includes!(source_reflection.name => includes)
+              else
+                scope.includes!(source_reflection.name)
+              end
+
               if joins = values[:joins]
                 scope.joins!(source_reflection.name => joins)
               end
diff --git a/activerecord/test/models/author.rb b/activerecord/test/models/author.rb
index 09958ca257..025d013fb4 100644
--- a/activerecord/test/models/author.rb
+++ b/activerecord/test/models/author.rb
@@ -21,7 +21,7 @@ class Author < ActiveRecord::Base
   end
   has_many :comments_containing_the_letter_e, through: :posts, source: :comments
   has_many :comments_with_order_and_conditions, -> { order("comments.body").where("comments.body like 'Thank%'") }, through: :posts, source: :comments
-  has_many :comments_with_include, -> { includes(:post) }, through: :posts, source: :comments
+  has_many :comments_with_include, -> { includes(:post).where(posts: { type: "Post" }) }, through: :posts, source: :comments
 
   has_many :first_posts
   has_many :comments_on_first_posts, -> { order("posts.id desc, comments.id asc") }, through: :first_posts, source: :comments