diff --git a/backend/src/board-store.ts b/backend/src/board-store.ts
index b460dafe8..3c82f1756 100644
--- a/backend/src/board-store.ts
+++ b/backend/src/board-store.ts
@@ -29,7 +29,7 @@ with allow_lists as (
 	  from board_access a
 	  where a.board_id = b.id
 	) as allow_list
-	from board b
+	from board b for update
 )
 select id,
     jsonb_set (content - 'accessPolicy', '{accessPolicy}', cast(case when allow_list is null then 'null' else (json_build_object('allowList', allow_list, 'publicRead', public_read, 'publicWrite', public_write)) end as jsonb)) as content
diff --git a/backend/src/compact-history.ts b/backend/src/compact-history.ts
index 151e07258..6546550e1 100644
--- a/backend/src/compact-history.ts
+++ b/backend/src/compact-history.ts
@@ -15,10 +15,13 @@ import {
     verifyContinuityFromMetas,
 } from "./board-store"
 import { inTransaction } from "./db"
+import { sleep } from "../../common/src/sleep"
 
 export async function quickCompactBoardHistory(id: Id) {
     let fallback = false
     const result = inTransaction(async (client) => {
+        // Lock the board to prevent loading the board while compacting
+        await client.query("select 1 from board where id=$1 for update", [id])
         const bundleMetas = await getBoardHistoryBundleMetas(client, id)
         if (bundleMetas.length === 0) return
         const consistent = verifyContinuityFromMetas(id, 0, bundleMetas)