diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index 0b7659811..7d6205cad 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "2.26.27",
+    "version": "2.26.28",
     "bin": "bin/hydrooj.js",
     "main": "dist/loader.js",
     "typings": "dist/loader.d.ts",
diff --git a/packages/hydrooj/src/handler/contest.ts b/packages/hydrooj/src/handler/contest.ts
index 4a2fa8647..adb6a3c78 100644
--- a/packages/hydrooj/src/handler/contest.ts
+++ b/packages/hydrooj/src/handler/contest.ts
@@ -337,7 +337,7 @@ class ContestDetailProblemSubmitHandler extends ContestProblemHandler {
     @param('lang', Types.Name)
     @param('code', Types.Content)
     async post(domainId: string, tid: ObjectID, lang: string, code: string) {
-        if (this.response.body.pdoc.config.langs && !this.response.body.pdoc.config.langs.includes('lang')) {
+        if (this.response.body.pdoc.config?.langs && !this.response.body.pdoc.config.langs.includes(lang)) {
             throw new BadRequestError('Language not allowed.');
         }
         await this.limitRate('add_record', 60, 10);
diff --git a/packages/hydrooj/src/handler/homework.ts b/packages/hydrooj/src/handler/homework.ts
index f61cad357..0f6798d18 100644
--- a/packages/hydrooj/src/handler/homework.ts
+++ b/packages/hydrooj/src/handler/homework.ts
@@ -196,7 +196,7 @@ class HomeworkDetailProblemSubmitHandler extends HomeworkDetailProblemHandler {
     @param('code', Types.Content)
     @param('lang', Types.Name)
     async post(domainId: string, tid: ObjectID, pid: number, code: string, lang: string) {
-        if (this.response.body.pdoc.config?.langs && !this.response.body.pdoc.config.langs.includes('lang')) {
+        if (this.response.body.pdoc.config?.langs && !this.response.body.pdoc.config.langs.includes(lang)) {
             throw new BadRequestError('Language not allowed.');
         }
         await this.limitRate('add_record', 60, 5);
diff --git a/packages/hydrooj/src/handler/problem.ts b/packages/hydrooj/src/handler/problem.ts
index dd94f948a..8a29f5aa4 100644
--- a/packages/hydrooj/src/handler/problem.ts
+++ b/packages/hydrooj/src/handler/problem.ts
@@ -275,7 +275,7 @@ export class ProblemSubmitHandler extends ProblemDetailHandler {
     @param('lang', Types.Name)
     @param('code', Types.Content)
     async post(domainId: string, lang: string, code: string) {
-        if (this.response.body.pdoc.config?.langs && !this.response.body.pdoc.config.langs.includes('lang')) {
+        if (this.response.body.pdoc.config?.langs && !this.response.body.pdoc.config.langs.includes(lang)) {
             throw new BadRequestError('Language not allowed.');
         }
         await this.limitRate('add_record', 60, 5);