1 files changed, 2 insertions, 1 deletions
diff --git a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
index 2ee5dbbd70..88ce03a3cd 100644
--- a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
@@ -27,7 +27,8 @@ module ActiveRecord
         end
 
         def stale_state
-          [super, owner[reflection.foreign_type].to_s]
+          foreign_key = super
+          foreign_key && [foreign_key.to_s, owner[reflection.foreign_type].to_s]
         end
     end
   end