diff --git a/kallithea/model/db.py b/kallithea/model/db.py
--- a/kallithea/model/db.py
+++ b/kallithea/model/db.py
@@ -2357,6 +2357,7 @@ class PullRequest(Base, BaseModel):
 class PullRequestReviewers(Base, BaseModel):
     __tablename__ = 'pull_request_reviewers'
     __table_args__ = (
+        Index('pull_request_reviewers_user_id_idx', 'user_id'),
         _table_args_default_dict,
     )