diff --git a/lib/jsonapi/resource.rb b/lib/jsonapi/resource.rb
index a5bb1d791..94c0c097c 100644
--- a/lib/jsonapi/resource.rb
+++ b/lib/jsonapi/resource.rb
@@ -324,7 +324,7 @@ def _replace_polymorphic_to_one_link(relationship_type, key_value, key_type, opt
       relationship = self.class._relationships[relationship_type.to_sym]
 
       _model.public_send("#{relationship.foreign_key}=", key_value)
-      _model.public_send("#{relationship.polymorphic_type}=", _model_class_name(key_type))
+      _model.public_send("#{relationship.polymorphic_type}=", self.class.model_name_for_type(key_type))
 
       @save_needed = true
 
@@ -404,12 +404,6 @@ def _replace_fields(field_data)
       :completed
     end
 
-    def _model_class_name(key_type)
-      type_class_name = key_type.to_s.classify
-      resource = self.class.resource_for(type_class_name)
-      resource ? resource._model_name.to_s : type_class_name
-    end
-
     class << self
       def inherited(subclass)
         subclass.abstract(false)
@@ -467,6 +461,12 @@ def resource_type_for(model)
         end
       end
 
+      def model_name_for_type(key_type)
+        type_class_name = key_type.to_s.classify
+        resource = resource_for(type_class_name)
+        resource ? resource._model_name.to_s : type_class_name
+      end
+
       attr_accessor :_attributes, :_relationships, :_type, :_model_hints
       attr_writer :_allowed_filters, :_paginator