diff --git a/lib/active_model/serializer/associations.rb b/lib/active_model/serializer/associations.rb
index 3165258b..6b4460e6 100644
--- a/lib/active_model/serializer/associations.rb
+++ b/lib/active_model/serializer/associations.rb
@@ -69,7 +69,7 @@ module ActiveModel
           if key = options[:key]
             key
           elsif embed_ids?
-            "#{@name.to_s.singularize}_ids".to_sym
+            id_key
           else
             @name
           end
@@ -83,6 +83,10 @@ module ActiveModel
           end
         end
 
+        def id_key
+          "#{@name.to_s.singularize}_ids".to_sym
+        end
+
         def serialize
           associated_object.map do |item|
             find_serializable(item).serializable_hash
@@ -96,9 +100,8 @@ module ActiveModel
         end
 
         def serialize_ids
-          ids_key = "#{@name.to_s.singularize}_ids".to_sym
-          if !options[:embed_key] && !source_serializer.respond_to?(@name.to_s) && source_serializer.object.respond_to?(ids_key)
-            source_serializer.object.read_attribute_for_serialization(ids_key)
+          if !options[:embed_key] && !source_serializer.respond_to?(@name.to_s) && source_serializer.object.respond_to?(id_key)
+            source_serializer.object.read_attribute_for_serialization(id_key)
           else
             associated_object.map do |item|
               item.read_attribute_for_serialization(embed_key)
@@ -134,7 +137,7 @@ module ActiveModel
           if key = options[:key]
             key
           elsif embed_ids? && !polymorphic?
-            "#{@name}_id".to_sym
+            id_key
           else
             @name
           end
@@ -148,6 +151,10 @@ module ActiveModel
           end
         end
 
+        def id_key
+          "#{@name}_id".to_sym
+        end
+
         def polymorphic_key
           associated_object.class.to_s.demodulize.underscore.to_sym
         end
@@ -172,8 +179,6 @@ module ActiveModel
         end
 
         def serialize_ids
-          id_key = "#{@name}_id".to_sym
-
           if polymorphic?
             if associated_object
               {