diff --git a/docker/backend/src/backend/api/schema/mutation.cr b/docker/backend/src/backend/api/schema/mutation.cr
index 6fce16d..358ce43 100644
--- a/docker/backend/src/backend/api/schema/mutation.cr
+++ b/docker/backend/src/backend/api/schema/mutation.cr
@@ -143,6 +143,8 @@ module Backend
         def create_vote(context : Context, input : VoteCreateInput) : Vote
           context.student!
 
+          raise "Teacher selection can't be empty" if input.teacher_ids.empty?
+
           skif = context.external.as(Db::Student).skif
           input.teacher_ids.each do |id|
             teacher = Db::Teacher.find(id)