diff --git a/backend/src/index.ts b/backend/src/index.ts
index c336ba5..e0efb21 100644
--- a/backend/src/index.ts
+++ b/backend/src/index.ts
@@ -2962,13 +2962,13 @@ app.post("/api/periods/:periodType/:period/close", requireUser, async (req, res)
         false AS ticket_closed
       FROM tickets t
       JOIN sessions s ON s.ticket_id = t.id
-      WHERE s.started_at >= $2::timestamptz AND s.started_at < $3::timestamptz
-        AND s.user_id = $4
+      WHERE s.started_at >= $1::timestamptz AND s.started_at < $2::timestamptz
+        AND s.user_id = $3
       GROUP BY t.id, t.ticket_number
       HAVING COUNT(*) FILTER (WHERE s.billing_status IS NULL) > 0
       ORDER BY t.ticket_number ASC;
     `,
-    [period.start, period.startIso, period.endIso, userId]
+    [period.startIso, period.endIso, userId]
   );
 
   if (blockersResult.rows.length > 0) {
diff --git a/backend/src/migrations.ts b/backend/src/migrations.ts
index 8c49f9d..0bb27c4 100644
--- a/backend/src/migrations.ts
+++ b/backend/src/migrations.ts
@@ -7,9 +7,25 @@ async function findMigrationAdmin() {
 
 async function ensureClosureOwnership(table: string, column: string, primaryKeyColumns: string[], adminId: string | null) {
   await query(`ALTER TABLE ${table} ADD COLUMN IF NOT EXISTS user_id BIGINT REFERENCES users(id);`);
+
   if (adminId) {
     await query(`UPDATE ${table} SET user_id = $1 WHERE user_id IS NULL;`, [adminId]);
   }
+
+  const duplicateMatchers = [...primaryKeyColumns, "user_id"]
+    .map((key) => `older.${key} IS NOT DISTINCT FROM newer.${key}`)
+    .join(" AND ");
+
+  await query(`
+    DELETE FROM ${table} older
+    USING ${table} newer
+    WHERE ${duplicateMatchers}
+      AND (
+        older.closed_at < newer.closed_at
+        OR (older.closed_at = newer.closed_at AND older.ctid < newer.ctid)
+      );
+  `);
+
   await query(`
     DO $$
     BEGIN