diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index dddb465c..8452eb4e 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -347,7 +347,7 @@ module ActiveModel
       return Enumerator.new {} unless object
 
       Enumerator.new do |y|
-        self.class._reflections.each do |key, reflection|
+        (@reflections ||= self.class._reflections.deep_dup).each do |key, reflection|
           next if reflection.excluded?(self)
           next unless include_directive.key?(key)
 
@@ -411,6 +411,6 @@ module ActiveModel
 
     protected
 
-    attr_accessor :instance_options
+    attr_accessor :instance_options, :reflections
   end
 end