diff --git a/lib/jsonapi/parser/resource.rb b/lib/jsonapi/parser/resource.rb
index c0c3708..fd99003 100644
--- a/lib/jsonapi/parser/resource.rb
+++ b/lib/jsonapi/parser/resource.rb
@@ -11,7 +11,7 @@ def self.parse!(document)
         Document.ensure!(document.is_a?(Hash),
                          'A JSON object MUST be at the root of every JSONAPI ' \
                          'request and response containing data.')
-        Document.ensure!(document.keys == ['data'].freeze &&
+        Document.ensure!(document.keys.include?('data') &&
                          document['data'].is_a?(Hash),
                          'The request MUST include a single resource object ' \
                          'as primary data.')