diff --git a/.rubocop.yml b/.rubocop.yml
index e7d729cc..8e00e2dc 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -47,3 +47,7 @@ Style/Documentation:
 
 Style/MultilineOperationIndentation:
   EnforcedStyle: indented
+
+Style/BlockDelimiters:
+  Enabled: true
+  EnforcedStyle: line_count_based
diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index 36ce4dfc..6e89b8b1 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -78,12 +78,6 @@ Style/AndOr:
   Exclude:
     - 'lib/active_model/serializer/lint.rb'
 
-# Offense count: 6
-# Cop supports --auto-correct.
-# Configuration parameters: EnforcedStyle, SupportedStyles, ProceduralMethods, FunctionalMethods, IgnoredMethods.
-Style/BlockDelimiters:
-  Enabled: false
-
 # Offense count: 46
 # Cop supports --auto-correct.
 # Configuration parameters: EnforcedStyle, SupportedStyles.
diff --git a/lib/active_model/serializer/adapter.rb b/lib/active_model/serializer/adapter.rb
index 832fe3f4..61a86e1c 100644
--- a/lib/active_model/serializer/adapter.rb
+++ b/lib/active_model/serializer/adapter.rb
@@ -58,12 +58,12 @@ module ActiveModel
           return adapter if adapter.is_a?(Class)
           adapter_name = adapter.to_s.underscore
           # 2. return if registered
-          adapter_map.fetch(adapter_name) {
+          adapter_map.fetch(adapter_name) do
             # 3. try to find adapter class from environment
             adapter_class = find_by_name(adapter_name)
             register(adapter_name, adapter_class)
             adapter_class
-          }
+          end
         rescue NameError, ArgumentError => e
           failure_message =
             "NameError: #{e.message}. Unknown adapter: #{adapter.inspect}. Valid adapters are: #{adapters}"
diff --git a/lib/active_model/serializer/adapter/json_api.rb b/lib/active_model/serializer/adapter/json_api.rb
index 3637ccb7..94571eaa 100644
--- a/lib/active_model/serializer/adapter/json_api.rb
+++ b/lib/active_model/serializer/adapter/json_api.rb
@@ -130,14 +130,11 @@ module ActiveModel
           end
         end
 
-        def included_resources(include_tree)
-          included = []
-
-          serializer.associations(include_tree).each do |association|
-            add_included_resources_for(association.serializer, include_tree[association.key], included)
-          end
-
-          included
+        def included_for(serializer)
+          included.flat_map do |inc|
+            association = serializer.associations.find { |assoc| assoc.key == inc.first }
+            _included_for(association.serializer, inc.second) if association
+          end.uniq
         end
 
         def add_included_resources_for(serializer, include_tree, included)
diff --git a/lib/active_model/serializer/array_serializer.rb b/lib/active_model/serializer/array_serializer.rb
index 7a5aed20..9c7b2b93 100644
--- a/lib/active_model/serializer/array_serializer.rb
+++ b/lib/active_model/serializer/array_serializer.rb
@@ -11,9 +11,9 @@ module ActiveModel
         @root = options[:root]
         @object = resources
         @serializers = resources.map do |resource|
-          serializer_class = options.fetch(:serializer) {
+          serializer_class = options.fetch(:serializer) do
             ActiveModel::Serializer.serializer_for(resource)
-          }
+          end
 
           if serializer_class.nil?
             fail NoSerializerError, "No serializer found for resource: #{resource.inspect}"
diff --git a/test/action_controller/serialization_test.rb b/test/action_controller/serialization_test.rb
index acf62a47..e9288d56 100644
--- a/test/action_controller/serialization_test.rb
+++ b/test/action_controller/serialization_test.rb
@@ -400,25 +400,25 @@ module ActionController
       end
 
       def test_warn_overridding_use_adapter_as_falsy_on_controller_instance
-        controller = Class.new(ImplicitSerializationTestController) {
+        controller = Class.new(ImplicitSerializationTestController) do
           def use_adapter?
             false
           end
-        }.new
-        assert_match(/adapter: false/, (capture(:stderr) {
+        end.new
+        assert_match(/adapter: false/, (capture(:stderr) do
           controller.get_serializer(Profile.new)
-        }))
+        end))
       end
 
       def test_dont_warn_overridding_use_adapter_as_truthy_on_controller_instance
-        controller = Class.new(ImplicitSerializationTestController) {
+        controller = Class.new(ImplicitSerializationTestController) do
           def use_adapter?
             true
           end
-        }.new
-        assert_equal '', (capture(:stderr) {
+        end.new
+        assert_equal '', (capture(:stderr) do
           controller.get_serializer(Profile.new)
-        })
+        end)
       end
     end
   end
diff --git a/test/capture_warnings.rb b/test/capture_warnings.rb
index 5acdb3a0..7a39e7c2 100644
--- a/test/capture_warnings.rb
+++ b/test/capture_warnings.rb
@@ -28,9 +28,9 @@ class CaptureWarnings
 
   # rubocop:disable Metrics/AbcSize
   def after_tests(lines)
-    app_warnings, other_warnings = lines.partition { |line|
+    app_warnings, other_warnings = lines.partition do |line|
       line.include?(app_root) && !line.include?(bundle_dir)
-    }
+    end
 
     header = "#{'-' * 22} app warnings: #{'-' * 22}"
     output.puts