diff --git a/app/lib/snail_mail/imb.rb b/app/lib/snail_mail/imb.rb
index f015eab..e213406 100644
--- a/app/lib/snail_mail/imb.rb
+++ b/app/lib/snail_mail/imb.rb
@@ -12,7 +12,7 @@ module SnailMail
       mailer_id = letter.usps_mailer_id&.mid
       return "" unless mailer_id
       serial_number = letter.imb_serial_number
-      routing_code = letter.address.us? ? letter.address.postal_code.gsub(/[^0-9]/, "") : nil # zip(+dpc?) but no dash
+      routing_code = letter.address.us? ? letter.address.postal_code&.gsub(/[^0-9]/, "") : nil # zip(+dpc?) but no dash
 
       routing_code = nil unless [5, 9, 11].include?(routing_code&.length)