diff --git a/lib/mongoid/grid_fs.rb b/lib/mongoid/grid_fs.rb
index 60ed44a..95eaaa0 100644
--- a/lib/mongoid/grid_fs.rb
+++ b/lib/mongoid/grid_fs.rb
@@ -366,7 +366,7 @@ def data
           end
 
           def base64
-            Array(to_s).pack('m')
+            Array(data).pack('m')
           end
 
           def data_uri(options = {})