diff --git a/app/models/log.rb b/app/models/log.rb
index 66e996892..d55289997 100644
--- a/app/models/log.rb
+++ b/app/models/log.rb
@@ -248,6 +248,11 @@ class Log < ApplicationRecord
   end
 
   def blank_compound_invalid_non_setup_fields!
+    if errors.attribute_names.include? :postcode_full
+      self.postcode_known = nil if lettings?
+      self.pcodenk = nil if sales?
+    end
+
     self.ppcodenk = nil if errors.attribute_names.include? :ppostcode_full
     self.previous_la_known = nil if errors.attribute_names.include? :prevloc
 
@@ -258,6 +263,8 @@ class Log < ApplicationRecord
       self.address_line2 = nil
       self.town_or_city = nil
       self.postcode_full = nil
+      self.postcode_known = nil if lettings?
+      self.pcodenk = nil if sales?
       self.county = nil
       process_postcode_changes!
     end