diff --git a/api/apps/restful_apis/file_api.py b/api/apps/restful_apis/file_api.py
index b67aa30ff..2815dd681 100644
--- a/api/apps/restful_apis/file_api.py
+++ b/api/apps/restful_apis/file_api.py
@@ -299,6 +299,13 @@ async def download(tenant_id: str = None, file_id: str = None):
         if not blob:
             b, n = File2DocumentService.get_storage_address(file_id=file_id)
             blob = await thread_pool_exec(settings.STORAGE_IMPL.get, b, n)
+        if not blob:
+            logging.warning(
+                "Download failed: empty blob after primary+fallback lookup (tenant_id=%s, file_id=%s)",
+                tenant_id,
+                file_id,
+            )
+            return get_error_data_result(message="This file is empty.")
 
         response = await make_response(blob)
         ext = re.search(r"\.([^.]+)$", file.name.lower())
diff --git a/test/testcases/test_web_api/test_file_app/test_file_routes_unit.py b/test/testcases/test_web_api/test_file_app/test_file_routes_unit.py
index c1ff639ac..b95592ad9 100644
--- a/test/testcases/test_web_api/test_file_app/test_file_routes_unit.py
+++ b/test/testcases/test_web_api/test_file_app/test_file_routes_unit.py
@@ -327,6 +327,22 @@ def test_download_falls_back_to_document_storage(monkeypatch):
     assert res.headers["ext"] == "txt"
 
 
+@pytest.mark.p2
+def test_download_missing_blob_returns_error(monkeypatch):
+    module = _load_file_api_module(monkeypatch)
+    storage_calls = []
+
+    def _get(bucket, location):
+        storage_calls.append((bucket, location))
+        return None
+
+    monkeypatch.setattr(module.settings, "STORAGE_IMPL", SimpleNamespace(get=_get))
+    res = _run(module.download("tenant1", "file1"))
+
+    assert storage_calls == [("bucket1", "path1"), ("bucket2", "path2")]
+    assert res["message"] == "This file is empty."
+
+
 @pytest.mark.p2
 def test_parent_and_ancestors_use_new_routes(monkeypatch):
     module = _load_file_api_module(monkeypatch)