diff --git a/app/models/attachment.rb b/app/models/attachment.rb
index 7096ca330..a918f4e0a 100644
--- a/app/models/attachment.rb
+++ b/app/models/attachment.rb
@@ -38,7 +38,7 @@ class Attachment < ApplicationRecord
     if container.is_a?(StudentWork) && author_id != User.current.id
       course = container&.homework_common&.course
       unless User.current.teacher_of_course?(course)
-        title = "#{Time.now.strftime('%Y-%m-%d %H:%M:%S')}_#{DCODES.sample(8).join}" + File.extname(filename)
+        title = "#{Time.now.strftime('%Y%m%d%H%M%S')}_#{DCODES.sample(8).join}" + File.extname(filename)
       end
     end
     title