diff --git a/Store/MongoDbStore.php b/Store/MongoDbStore.php
index a7d9b46..bccfdf1 100644
--- a/Store/MongoDbStore.php
+++ b/Store/MongoDbStore.php
@@ -168,7 +168,7 @@ private function skimUri(string $uri): string
      *
      * Alternatively the TTL index can be created manually on the database:
      *
-     *  db.lock.ensureIndex(
+     *  db.lock.createIndex(
      *      { "expires_at": 1 },
      *      { "expireAfterSeconds": 0 }
      *  )