diff --git a/changes/sync-monthly-rollup-timezone.md b/changes/sync-monthly-rollup-timezone.md
new file mode 100644
index 00000000..bc4c7aca
--- /dev/null
+++ b/changes/sync-monthly-rollup-timezone.md
@@ -0,0 +1,4 @@
+type: fixed
+area: sync
+
+- Fixed stats sync copying a remote daily rollup that should have been recomputed when the day was the 1st of a month and the machine was on a negative UTC offset (the Americas), which could leave that day's totals wrong after a sync. The rollup day is now read back at local noon instead of UTC midnight, so it always resolves to the correct civil month.
diff --git a/src/core/services/stats-sync/merge-rollups.ts b/src/core/services/stats-sync/merge-rollups.ts
index ee91e339..3d007898 100644
--- a/src/core/services/stats-sync/merge-rollups.ts
+++ b/src/core/services/stats-sync/merge-rollups.ts
@@ -193,10 +193,13 @@ export function copyRemoteOnlyRollups(
   const localMonthSessions = local.query(
     `SELECT 1 FROM imm_sessions WHERE video_id = ? AND ${LOCAL_MONTH_EXPR} = ? LIMIT 1`,
   );
+  // rollup_day is a *local* epoch day, so anchor it at local noon (+43200)
+  // before reading its month back: plain UTC midnight lands in the previous
+  // civil month for the 1st of a month at any negative UTC offset.
   const localMonthSessionsForDay = local.query(
     `SELECT 1 FROM imm_sessions
      WHERE video_id = ?
-       AND ${LOCAL_MONTH_EXPR} = CAST(strftime('%Y%m', CAST(? AS INTEGER) * 86400, 'unixepoch', 'localtime') AS INTEGER)
+       AND ${LOCAL_MONTH_EXPR} = CAST(strftime('%Y%m', CAST(? AS INTEGER) * 86400 + 43200, 'unixepoch', 'localtime') AS INTEGER)
      LIMIT 1`,
   );
   const insertDaily = local.query(