diff --git a/lib/searchkick/record_data.rb b/lib/searchkick/record_data.rb
index 2cc101d..d9212cb 100644
--- a/lib/searchkick/record_data.rb
+++ b/lib/searchkick/record_data.rb
@@ -58,7 +58,7 @@ module Searchkick
         end
       end
       EXCLUDED_ATTRIBUTES.each do |attr|
-        source.delete(attr)
+        raise Searchkick::Error, "Cannot index a field with name: #{attr}" if source[attr]
       end
 
       # conversions
--
libgit2 0.21.0