diff --git a/packages/hydrojudge/package.json b/packages/hydrojudge/package.json
index 2873ea252..2dca96d5c 100644
--- a/packages/hydrojudge/package.json
+++ b/packages/hydrojudge/package.json
@@ -1,7 +1,7 @@
 {
     "name": "@hydrooj/hydrojudge",
     "bin": "bin/hydrojudge.js",
-    "version": "2.11.8",
+    "version": "2.11.9",
     "main": "package.json",
     "author": "undefined <i@undefined.moe>",
     "repository": "https://github.com/hydro-dev/Hydro.git",
diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index 4dc9c7885..103457235 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "2.39.20",
+    "version": "2.39.21",
     "bin": "bin/hydrooj.js",
     "main": "src/loader",
     "module": "src/loader",
diff --git a/packages/hydrooj/src/handler/problem.ts b/packages/hydrooj/src/handler/problem.ts
index 508ae52e2..bf50d77c5 100644
--- a/packages/hydrooj/src/handler/problem.ts
+++ b/packages/hydrooj/src/handler/problem.ts
@@ -45,6 +45,7 @@ registerValue('Problem', [
     ['domainId', 'String!'],
     ['docId', 'Int!'],
     ['docType', 'Int!'],
+    ['pid', 'String'],
     ['title', 'String!'],
     ['content', 'String!'],
     ['config', 'String!'],
diff --git a/packages/ui-default/components/zipDownloader/index.js b/packages/ui-default/components/zipDownloader/index.js
index fa289e42d..e6b4de908 100644
--- a/packages/ui-default/components/zipDownloader/index.js
+++ b/packages/ui-default/components/zipDownloader/index.js
@@ -5,7 +5,7 @@ import pipeStream from 'vj/utils/pipeStream';
 import i18n from 'vj/utils/i18n';
 import request from 'vj/utils/request';
 import Notification from 'vj/components/notification';
-import api from 'vj/utils/api';
+import api, { gql } from 'vj/utils/api';
 
 let isBeforeUnloadTriggeredByLibrary = !window.isSecureContext;
 function onBeforeUnload(e) {
@@ -21,11 +21,15 @@ if (window.location.protocol === 'https:'
   streamsaver.mitm = '/streamsaver/mitm.html';
 }
 
-export default async function download(name, targets) {
-  if (!window.WritableStream) {
-    window.WritableStream = (await import('web-streams-polyfill/dist/ponyfill.es6')).WritableStream;
+const waitForWritableStream = window.WritableStream
+  ? Promise.resolve()
+  : import('web-streams-polyfill/dist/ponyfill.es6').then(({ WritableStream }) => {
+    window.WritableStream = WritableStream;
     streamsaver.WritableStream = window.WritableStream;
-  }
+  });
+
+export default async function download(name, targets) {
+  await waitForWritableStream;
   const fileStream = streamsaver.createWriteStream(name);
   let i = 0;
   const zipStream = createZipStream({
@@ -68,9 +72,8 @@ export async function downloadProblemSet(pids, name = 'Export') {
   const targets = [];
   try {
     for (const pid of pids) {
-      const { pdoc } = await request.get(`/d/${UiContext.domainId}/api`);
-      await api(gql`
-        problem(id: ${pid}) {
+      const pdoc = await api(gql`
+        problem(id: ${+pid}) {
           pid
           owner
           title
@@ -85,7 +88,7 @@ export async function downloadProblemSet(pids, name = 'Export') {
             name
           }
         }
-      `);
+      `, ['data', 'problem']);
       targets.push({
         filename: `${pid}/problem.yaml`,
         content: dump({
@@ -117,7 +120,7 @@ export async function downloadProblemSet(pids, name = 'Export') {
     }
     await download(`${name}.zip`, targets);
   } catch (e) {
-    Notification.warn(`${e.error.message} ${e.error.params[0]}`);
+    Notification.warn(`${e.error?.message} ${e.error?.params?.[0]}`);
   }
 }
 
diff --git a/packages/ui-default/utils/api.ts b/packages/ui-default/utils/api.ts
index 2a70ae302..cebf72b03 100644
--- a/packages/ui-default/utils/api.ts
+++ b/packages/ui-default/utils/api.ts
@@ -3,7 +3,7 @@ import request from './request';
 export default async (q: string, path: string[] = []) => {
   let query = q.trim();
   if (!query.startsWith('query')) query = `query{${query}}`;
-  const res = await request.post('/api', { query });
+  const res = await request.post(`/d/${UiContext.domainId}/api`, { query });
   if (res.errors) throw new Error(res.errors[0].message);
   let cursor = res;
   for (const p of path) {