diff --git a/lib/excerpt_parser.rb b/lib/excerpt_parser.rb
index 4a2f483f36..054a123401 100644
--- a/lib/excerpt_parser.rb
+++ b/lib/excerpt_parser.rb
@@ -97,7 +97,7 @@ class ExcerptParser < Nokogiri::XML::SAX::Document
 
     when "aside"
       attributes = Hash[*attributes.flatten]
-      unless (@keep_onebox_source || @keep_onebox_body) && attributes['class'].include?('onebox')
+      unless (@keep_onebox_source || @keep_onebox_body) && attributes['class']&.include?('onebox')
         @in_quote = true
       end