diff --git a/src/models/poll-vote.ts b/src/models/poll-vote.ts
index 4390e000c3..b8aceae3b0 100644
--- a/src/models/poll-vote.ts
+++ b/src/models/poll-vote.ts
@@ -4,6 +4,7 @@ import db from '../db/mongodb';
 const PollVote = db.get<IPollVote>('pollVotes');
 PollVote.createIndex('userId');
 PollVote.createIndex('noteId');
+PollVote.createIndex(['userId', 'noteId'], { unique: true });
 export default PollVote;
 
 export interface IPollVote {