diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index 4b671f920..a6a984fd8 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -29,7 +29,6 @@
         "fs-extra": "^11.1.0",
         "graphql": "^16.6.0",
         "graphql-scalars": "1.20.1",
-        "isbinaryfile": "^5.0.0",
         "js-yaml": "^4.1.0",
         "koa": "^2.14.1",
         "koa-body": "^6.0.1",
diff --git a/packages/hydrooj/src/handler/problem.ts b/packages/hydrooj/src/handler/problem.ts
index b7fcbc79d..c0f7d3a40 100644
--- a/packages/hydrooj/src/handler/problem.ts
+++ b/packages/hydrooj/src/handler/problem.ts
@@ -1,6 +1,5 @@
 import AdmZip from 'adm-zip';
 import { readFile, statSync } from 'fs-extra';
-import { isBinaryFile } from 'isbinaryfile';
 import {
     escapeRegExp, flattenDeep, intersection, pick, uniqBy,
 } from 'lodash';
@@ -524,8 +523,9 @@ export class ProblemSubmitHandler extends ProblemDetailHandler {
             if (!file || file.size === 0) throw new ValidationError('code');
             const sizeLimit = config.type === 'submit_answer' ? 128 * 1024 * 1024 : 65535;
             if (file.size > sizeLimit) throw new ValidationError('file');
-            if (config.type !== 'submit_answer' || (file.size < 65535 && !await isBinaryFile(file.filepath, file.size))) {
+            if (file.size < 65535 && !file.filepath.endsWith('.zip')) {
                 // TODO auto detect & convert encoding
+                // TODO submission file shape
                 code = await readFile(file.filepath, 'utf-8');
             } else {
                 const id = nanoid();