diff --git a/app/models/lettings_log.rb b/app/models/lettings_log.rb
index d8e27daf5..2d29fb6db 100644
--- a/app/models/lettings_log.rb
+++ b/app/models/lettings_log.rb
@@ -649,6 +649,7 @@ class LettingsLog < Log
     super
 
     self.postcode_known = nil if errors.attribute_names.include? :postcode_full
+    self.ppcodenk = nil if errors.attribute_names.include? :ppostcode_full
 
     if errors.of_kind?(:earnings, :under_hard_min)
       self.incfreq = nil