diff --git a/app/models/course.rb b/app/models/course.rb
index 0c140cf..7d4b739 100644
--- a/app/models/course.rb
+++ b/app/models/course.rb
@@ -86,6 +86,7 @@ class Course < ApplicationRecord
   end
 
   def fill_in_default_live_video_url!
-    lectures.where(live_video_url: nil).update!(live_video_url: self.default_live_video_url)
+    raise "No default live video URL set" if self.default_live_video_url.nil?
+    lectures.where(live_video_url: nil).update_all!(live_video_url: self.default_live_video_url)
   end
 end