diff --git a/elasticsearch-model/lib/elasticsearch/model/indexing.rb b/elasticsearch-model/lib/elasticsearch/model/indexing.rb
index 360b8ea85..948c7b62a 100644
--- a/elasticsearch-model/lib/elasticsearch/model/indexing.rb
+++ b/elasticsearch-model/lib/elasticsearch/model/indexing.rb
@@ -336,7 +336,7 @@ def delete_document(options={})
         def update_document(options={})
           if changed_attributes = self.instance_variable_get(:@__changed_attributes)
             attributes = if respond_to?(:as_indexed_json)
-              changed_attributes.select { |k,v| self.as_indexed_json.keys.include? k }
+              changed_attributes.select { |k,v| self.as_indexed_json.keys.map(&:to_s).include? k.to_s }
             else
               changed_attributes
             end