diff --git a/lib/ahoy_email/processor.rb b/lib/ahoy_email/processor.rb
index 1daf646..8ad17ed 100644
--- a/lib/ahoy_email/processor.rb
+++ b/lib/ahoy_email/processor.rb
@@ -95,9 +95,9 @@ def track_links
     def parser_class
       case options[:html5]
       when true
-        Nokogiri::HTML5
+        Nokogiri::HTML5::Document
       when false
-        Nokogiri::HTML4
+        Nokogiri::HTML4::Document
       else
         Nokogiri::HTML::Document
       end