diff --git a/lib/jsonapi/active_relation_retrieval.rb b/lib/jsonapi/active_relation_retrieval.rb
index af4e62d1..2ee2e026 100644
--- a/lib/jsonapi/active_relation_retrieval.rb
+++ b/lib/jsonapi/active_relation_retrieval.rb
@@ -262,7 +262,7 @@ def find_fragments(filters, options = {})
       def find_related_fragments(source_fragment, relationship, options = {})
         if relationship.polymorphic? # && relationship.foreign_key_on == :self
           source_resource_klasses = if relationship.foreign_key_on == :self
-                                      relationship.class.polymorphic_types(relationship.name).collect do |polymorphic_type|
+                                      relationship.polymorphic_types.collect do |polymorphic_type|
                                         resource_klass_for(polymorphic_type)
                                       end
                                     else
@@ -284,7 +284,7 @@ def find_related_fragments(source_fragment, relationship, options = {})
       def find_included_fragments(source_fragments, relationship, options)
         if relationship.polymorphic? # && relationship.foreign_key_on == :self
           source_resource_klasses = if relationship.foreign_key_on == :self
-                                      relationship.class.polymorphic_types(relationship.name).collect do |polymorphic_type|
+                                      relationship.polymorphic_types.collect do |polymorphic_type|
                                         resource_klass_for(polymorphic_type)
                                       end
                                     else
diff --git a/lib/jsonapi/configuration.rb b/lib/jsonapi/configuration.rb
index e739b722..dce8b9e3 100644
--- a/lib/jsonapi/configuration.rb
+++ b/lib/jsonapi/configuration.rb
@@ -13,6 +13,7 @@ class Configuration
                 :warn_on_route_setup_issues,
                 :warn_on_missing_routes,
                 :warn_on_performance_issues,
+                :warn_on_eager_loading_disabled,
                 :default_allow_include_to_one,
                 :default_allow_include_to_many,
                 :allow_sort,
@@ -67,6 +68,7 @@ def initialize
       self.warn_on_route_setup_issues = true
       self.warn_on_missing_routes = true
       self.warn_on_performance_issues = true
+      self.warn_on_eager_loading_disabled = true
 
       # :none, :offset, :paged, or a custom paginator name
       self.default_paginator = :none
@@ -326,6 +328,8 @@ def allow_include=(allow_include)
 
     attr_writer :warn_on_performance_issues
 
+    attr_writer :warn_on_eager_loading_disabled
+
     attr_writer :use_relationship_reflection
 
     attr_writer :resource_cache
diff --git a/lib/jsonapi/relationship.rb b/lib/jsonapi/relationship.rb
index 1378d8e7..51be3719 100644
--- a/lib/jsonapi/relationship.rb
+++ b/lib/jsonapi/relationship.rb
@@ -19,10 +19,11 @@ def initialize(name, options = {})
       @parent_resource = options[:parent_resource]
       @relation_name = options[:relation_name]
       @polymorphic = options.fetch(:polymorphic, false) == true
-      @polymorphic_types = options[:polymorphic_types]
+      @polymorphic_types_override = options[:polymorphic_types]
+
       if options[:polymorphic_relations]
         JSONAPI.configuration.deprecate('Use polymorphic_types instead of polymorphic_relations')
-        @polymorphic_types ||= options[:polymorphic_relations]
+        @polymorphic_types_override ||= options[:polymorphic_relations]
       end
 
       use_related_resource_records_for_joins_default = if options[:relation_name]
@@ -86,16 +87,27 @@ def inverse_relationship
       @inverse_relationship
     end
 
-    def self.polymorphic_types(name)
-      ::JSONAPI::Utils::PolymorphicTypesLookup.polymorphic_types(name)
+    def polymorphic_types
+      return @polymorphic_types if @polymorphic_types
+
+      types = @polymorphic_types_override
+      types ||= ::JSONAPI::Utils::PolymorphicTypesLookup.polymorphic_types(_relation_name)
+
+      @polymorphic_types = types&.map { |t| t.to_s.pluralize } || []
+
+      if @polymorphic_types.blank?
+        warn "[POLYMORPHIC TYPE] No polymorphic types set or found for #{parent_resource.name} #{_relation_name}"
+      end
+
+      @polymorphic_types
     end
 
     def resource_types
-      if polymorphic? && belongs_to?
-        @polymorphic_types ||= self.class.polymorphic_types(_relation_name).collect { |t| t.pluralize }
-      else
-        [resource_klass._type.to_s.pluralize]
-      end
+      @resource_types ||= if polymorphic?
+                            polymorphic_types
+                          else
+                            [resource_klass._type.to_s.pluralize]
+                          end
     end
 
     def type
@@ -191,11 +203,7 @@ def polymorphic_type
       end
 
       def setup_implicit_relationships_for_polymorphic_types(exclude_linkage_data: true)
-        types = self.class.polymorphic_types(_relation_name)
-        unless types.present?
-          warn "[POLYMORPHIC TYPE] No polymorphic types found for #{parent_resource.name} #{_relation_name}"
-          return
-        end
+        types = polymorphic_types
 
         types.each do |type|
           parent_resource.has_one(type.to_s.underscore.singularize,
diff --git a/lib/jsonapi/resources/railtie.rb b/lib/jsonapi/resources/railtie.rb
index 02050879..920e88b1 100644
--- a/lib/jsonapi/resources/railtie.rb
+++ b/lib/jsonapi/resources/railtie.rb
@@ -19,8 +19,12 @@ class Railtie < ::Rails::Railtie
           }
       end
 
-      initializer "jsonapi_resources.initialize", after: :initialize do
-        JSONAPI::Utils::PolymorphicTypesLookup.polymorphic_types_lookup_clear!
+      config.before_initialize do
+        if !Rails.application.config.eager_load && ::JSONAPI::configuration.warn_on_eager_loading_disabled
+          warn 'WARNING: jsonapi-resources may not load polymorphic types when Rails `eager_load` is disabled. ' \
+                 'Polymorphic types may be set per relationship . This warning may be disable in the configuration ' \
+                 'by setting `warn_on_eager_loading_disabled` to false.'
+        end
       end
     end
   end