diff --git a/app/controllers/exercises_controller.rb b/app/controllers/exercises_controller.rb
index 750028c0..8a9ed527 100644
--- a/app/controllers/exercises_controller.rb
+++ b/app/controllers/exercises_controller.rb
@@ -123,7 +123,7 @@ class ExercisesController < ApplicationController
     uuid = params[:uuid]
     exercise = Exercise.find_by(uuid: uuid)
 
-    return render json: {exercise_found: false, message: 'no_exercise'} if exercise.nil?
+    return render json: {exercise_found: false, message: t('exercises.export_codeharbor.check.no_exercise')} if exercise.nil?
 
     render json: {exercise_found: true, message: 'exercise found, be careful when overwriting or else!'}
   end
@@ -136,13 +136,14 @@ class ExercisesController < ApplicationController
     user = user_for_oauth2_request
     return render json: {}, status: 401 if user.nil?
 
-    exercise = ProformaService::Import.call(zip: tempfile, user: user)
-    if exercise.save
-      render json: {}, status: 201
-    else
-      logger.info(exercise.errors.full_messages)
-      render json: {}, status: 400
+    exercise = nil
+    ActiveRecord::Base.transaction do
+      exercise = ::ProformaService::Import.call(zip: tempfile, user: user)
+      exercise.save!
+      return render json: {}, status: 201
     end
+    logger.info(exercise.errors.full_messages)
+    render json: {}, status: 400
   end
 
   def user_for_oauth2_request
diff --git a/app/models/code_ocean/file.rb b/app/models/code_ocean/file.rb
index a68b585b..91ad6e54 100644
--- a/app/models/code_ocean/file.rb
+++ b/app/models/code_ocean/file.rb
@@ -7,6 +7,7 @@ module CodeOcean
     def validate(record)
       existing_files = File.where(name: record.name, path: record.path, file_type_id: record.file_type_id,
                                   context_id: record.context_id, context_type: record.context_type).to_a
+
       unless existing_files.empty?
         if (not record.context.is_a?(Exercise)) || (record.context.new_record?)
           record.errors[:base] << 'Duplicate'
diff --git a/app/models/exercise.rb b/app/models/exercise.rb
index 05e69dcf..f975c45e 100644
--- a/app/models/exercise.rb
+++ b/app/models/exercise.rb
@@ -35,13 +35,13 @@ class Exercise < ApplicationRecord
   validates :public, boolean_presence: true
   validates :title, presence: true
   validates :token, presence: true, uniqueness: true
+  validates_uniqueness_of :uuid
 
   @working_time_statistics = nil
   attr_reader :working_time_statistics
 
   MAX_EXERCISE_FEEDBACKS = 20
 
-
   def average_percentage
     if average_score and maximum_score != 0.0 and submissions.exists?(cause: 'submit')
       (average_score / maximum_score * 100).round(2)
diff --git a/app/services/proforma_service/import.rb b/app/services/proforma_service/import.rb
index a4558870..7ab31055 100644
--- a/app/services/proforma_service/import.rb
+++ b/app/services/proforma_service/import.rb
@@ -11,8 +11,12 @@ module ProformaService
       if single_task?
         importer = Proforma::Importer.new(@zip)
         @task = importer.perform
-        exercise = ConvertTaskToExercise.call(task: @task, user: @user)
-        exercise.save!
+
+        exercise = Exercise.find_by(uuid: @task.uuid)
+        exercise_files = exercise&.files&.to_a
+
+        exercise = ConvertTaskToExercise.call(task: @task, user: @user, exercise: exercise)
+        exercise_files&.each(&:destroy) # feels suboptimal
 
         exercise
       else
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 6b8b243f..af6f191d 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -317,9 +317,11 @@ en:
     editor_file_tree:
       file_root: Files
     export_codeharbor:
+      check:
+        no_exercise: No exercise found
+      fail: Failed to push the exercise to CodeHarbor.
       label: Export to Codeharbor
       success: Successfully pushed the exercise to CodeHarbor.
-      fail: Failed to push the exercise to CodeHarbor.
     file_form:
       hints:
         feedback_message: This message is used as a hint for failing tests.