diff --git a/jsonapi-resources.gemspec b/jsonapi-resources.gemspec
index 65372c9f..f6b2f8af 100644
--- a/jsonapi-resources.gemspec
+++ b/jsonapi-resources.gemspec
@@ -28,6 +28,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'concurrent-ruby-ext'
   spec.add_development_dependency 'database_cleaner'
   spec.add_development_dependency 'hashie'
+  spec.add_development_dependency 'sorted_set'
   spec.add_dependency 'activerecord', '>= 5.1'
   spec.add_dependency 'railties', '>= 5.1'
   spec.add_dependency 'concurrent-ruby'
diff --git a/lib/jsonapi/active_relation_retrieval.rb b/lib/jsonapi/active_relation_retrieval.rb
index 1e1a72fb..f331bd59 100644
--- a/lib/jsonapi/active_relation_retrieval.rb
+++ b/lib/jsonapi/active_relation_retrieval.rb
@@ -271,7 +271,7 @@ def find_related_fragments(source_fragment, relationship, options = {})
           source_resource_klasses.each do |resource_klass|
             inverse_direct_relationship = _relationship(resource_klass._type.to_s.singularize)
 
-            fragments.merge!(resource_klass.find_related_fragments_from_inverse([source_fragment], inverse_direct_relationship, options, true))
+            fragments.merge!(resource_klass.find_related_fragments_from_inverse([source_fragment], inverse_direct_relationship, options, false))
           end
           fragments
         else
@@ -317,9 +317,16 @@ def find_related_fragments_from_inverse(source, source_relationship, options, co
         linkage_relationships = to_one_relationships_for_linkage(include_directives[:include_related])
 
         sort_criteria = []
-        options[:sort_criteria].try(:each) do |sort|
-          field = sort[:field].to_s == 'id' ? _primary_key : sort[:field]
-          sort_criteria << { field: field, direction: sort[:direction] }
+
+        # Do not sort the related_fragments. This can be keyed off `connect_source_identity` to indicate whether this
+        # is a related resource primary step vs. an include step.
+        sort_related_fragments = !connect_source_identity
+
+        if sort_related_fragments
+          options[:sort_criteria].try(:each) do |sort|
+            field = sort[:field].to_s == 'id' ? _primary_key : sort[:field]
+            sort_criteria << { field: field, direction: sort[:direction] }
+          end
         end
 
         join_manager = ActiveRelation::JoinManager.new(resource_klass: self,
diff --git a/lib/jsonapi/configuration.rb b/lib/jsonapi/configuration.rb
index 1d2c235e..b9f4b772 100644
--- a/lib/jsonapi/configuration.rb
+++ b/lib/jsonapi/configuration.rb
@@ -43,7 +43,8 @@ class Configuration
                 :resource_cache_usage_report_function,
                 :default_exclude_links,
                 :default_resource_retrieval_strategy,
-                :use_related_resource_records_for_joins
+                :use_related_resource_records_for_joins,
+                :related_identities_set
 
     def initialize
       #:underscored_key, :camelized_key, :dasherized_key, or custom
@@ -182,6 +183,13 @@ def initialize
       # This setting allows included resources to account for permission scopes. It can be overridden explicitly per
       # relationship. Furthermore, specifying a `relation_name` on a relationship will cause this setting to be ignored.
       self.use_related_resource_records_for_joins = true
+
+      # Collect the include keys into a Set or a SortedSet. SortedSet carries a small performance cost in the rails app
+      # but produces consistent and more human navigable result sets.
+      # To use SortedSet be sure to add `sorted_set` to your Gemfile and the following two lines to your JR initializer:
+      # require 'sorted_set'
+      # config.related_identities_set = SortedSet
+      self.related_identities_set = Set
     end
 
     def cache_formatters=(bool)
@@ -327,6 +335,8 @@ def allow_include=(allow_include)
     attr_writer :default_resource_retrieval_strategy
 
     attr_writer :use_related_resource_records_for_joins
+
+    attr_writer :related_identities_set
   end
 
   class << self
diff --git a/lib/jsonapi/resource_fragment.rb b/lib/jsonapi/resource_fragment.rb
index c354f9aa..0149f1ee 100644
--- a/lib/jsonapi/resource_fragment.rb
+++ b/lib/jsonapi/resource_fragment.rb
@@ -25,7 +25,7 @@ def initialize(identity, resource: nil, cache: nil, primary: false)
       @primary = primary
 
       @related = {}
-      @related_from = Set.new
+      @related_from = JSONAPI.configuration.related_identities_set.new
     end
 
     def initialize_related(relationship_name)
diff --git a/lib/jsonapi/resource_set.rb b/lib/jsonapi/resource_set.rb
index f4d6186f..e5846994 100644
--- a/lib/jsonapi/resource_set.rb
+++ b/lib/jsonapi/resource_set.rb
@@ -180,7 +180,7 @@ def flatten_resource_tree(resource_tree, flattened_tree = {})
         flattened_tree[resource_klass][id][:resource] ||= fragment.resource if fragment.resource
 
         fragment.related.try(:each_pair) do |relationship_name, related_rids|
-          flattened_tree[resource_klass][id][:relationships][relationship_name] ||= Set.new
+          flattened_tree[resource_klass][id][:relationships][relationship_name] ||= JSONAPI.configuration.related_identities_set.new
           flattened_tree[resource_klass][id][:relationships][relationship_name].merge(related_rids)
         end
       end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 834c8577..b92d8428 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -39,6 +39,9 @@
 
 JSONAPI.configure do |config|
   config.json_key_format = :camelized_key
+
+  require 'sorted_set'
+  config.related_identities_set = SortedSet
 end
 
 ActiveSupport::Deprecation.silenced = true