diff --git a/video-gen-api/alembic/versions/2026070902_add_generated_date_expression_indexes.py b/video-gen-api/alembic/versions/2026070902_add_generated_date_expression_indexes.py
index 8520a8c6..f71fafa5 100644
--- a/video-gen-api/alembic/versions/2026070902_add_generated_date_expression_indexes.py
+++ b/video-gen-api/alembic/versions/2026070902_add_generated_date_expression_indexes.py
@@ -24,16 +24,19 @@ def upgrade() -> None:
     # ========================================
     # 2026-07-09 - 生成记录表增加日期表达式索引
     # ========================================
+    # 使用 (generated_at AT TIME ZONE 'UTC')::date 而非 date(generated_at)，
+    # 因为 date(timestamp with time zone) 在 PostgreSQL 中是 STABLE（依赖会话时区），
+    # 不能用于索引表达式；转为无时区时间戳后再转 date 才是 IMMUTABLE。
     op.create_index(
         'idx_chat_generation_tasks_generated_date',
         'chat_generation_tasks',
-        [sa.text("date(generated_at)")],
+        [sa.text("(generated_at AT TIME ZONE 'UTC')::date")],
         unique=False,
     )
     op.create_index(
         'idx_generation_records_generated_date',
         'generation_records',
-        [sa.text("date(generated_at)")],
+        [sa.text("(generated_at AT TIME ZONE 'UTC')::date")],
         unique=False,
     )