diff --git a/app/models/exercise.rb b/app/models/exercise.rb
index 80725981..53a3ee26 100644
--- a/app/models/exercise.rb
+++ b/app/models/exercise.rb
@@ -155,8 +155,6 @@ def before_publication
     end
   end
 
-  protected
-
   def has_questions
     return unless questions.first.nil?
     errors.add(:questions, "can't be blank")
diff --git a/db/migrate/20220302162344_create_slug_tags.rb b/db/migrate/20220302162344_create_slug_tags.rb
index 48cc1355..3732575a 100644
--- a/db/migrate/20220302162344_create_slug_tags.rb
+++ b/db/migrate/20220302162344_create_slug_tags.rb
@@ -4,8 +4,8 @@ class CreateSlugTags < ActiveRecord::Migration[6.1]
   def up
     Exercise.preload(:publication).in_batches(of: 100, load: true) do |exercises|
       Exercise.transaction do
-        exercises.each(&:save) # creates the slug tags but does not set updated_at
-        exercises.update_all(updated_at: Time.current) # invalidates the exercise cache
+        exercises.each(&:set_slug_tags)
+        exercises.update_all updated_at: Time.current
       end
     end
   end