3 files changed, 37 insertions, 2 deletions
diff --git a/activerecord/lib/active_record/relation/merger.rb b/activerecord/lib/active_record/relation/merger.rb
index dd8f0aa298..0b38666ce9 100644
--- a/activerecord/lib/active_record/relation/merger.rb
+++ b/activerecord/lib/active_record/relation/merger.rb
@@ -87,8 +87,8 @@ module ActiveRecord
         return if other.preload_values.empty? && other.includes_values.empty?
 
         if other.klass == relation.klass
-          relation.preload! other.preload_values unless other.preload_values.empty?
-          relation.includes! other.includes_values unless other.includes_values.empty?
+          relation.preload!(*other.preload_values) unless other.preload_values.empty?
+          relation.includes!(other.includes_values) unless other.includes_values.empty?
         else
           reflection = relation.klass.reflect_on_all_associations.find do |r|
             r.class_name == other.klass.name
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index acbf85d398..5f48c2b40f 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -647,6 +647,25 @@ class RelationTest < ActiveRecord::TestCase
     end
   end
 
+  def test_preloading_with_associations_default_scopes_and_merges
+    post = Post.create! title: 'Uhuu', body: 'body'
+    reader = Reader.create! post_id: post.id, person_id: 1
+
+    post_rel = PostWithPreloadDefaultScope.preload(:readers).joins(:readers).where(title: 'Uhuu')
+    result_post = PostWithPreloadDefaultScope.all.merge(post_rel).to_a.first
+
+    assert_no_queries do
+      assert_equal [reader], result_post.readers.to_a
+    end
+
+    post_rel = PostWithIncludesDefaultScope.includes(:readers).where(title: 'Uhuu')
+    result_post = PostWithIncludesDefaultScope.all.merge(post_rel).to_a.first
+
+    assert_no_queries do
+      assert_equal [reader], result_post.readers.to_a
+    end
+  end
+
   def test_loading_with_one_association
     posts = Post.preload(:comments)
     post = posts.find { |p| p.id == 1 }
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index 052b1c9690..10f13b67da 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -208,6 +208,22 @@ class PostWithDefaultScope < ActiveRecord::Base
   default_scope { order(:title) }
 end
 
+class PostWithPreloadDefaultScope < ActiveRecord::Base
+  self.table_name = 'posts'
+
+  has_many :readers, foreign_key: 'post_id'
+
+  default_scope { preload(:readers) }
+end
+
+class PostWithIncludesDefaultScope < ActiveRecord::Base
+  self.table_name = 'posts'
+
+  has_many :readers, foreign_key: 'post_id'
+
+  default_scope { includes(:readers) }
+end
+
 class SpecialPostWithDefaultScope < ActiveRecord::Base
   self.table_name = 'posts'
   default_scope { where(:id => [1, 5,6]) }