diff --git a/.changeset/smart-melons-shop.md b/.changeset/smart-melons-shop.md
new file mode 100644
index 00000000000..e998cdef549
--- /dev/null
+++ b/.changeset/smart-melons-shop.md
@@ -0,0 +1,10 @@
+---
+"@logto/phrases": patch
+"@logto/core": patch
+---
+
+Fix file upload API.
+
+The `koa-body` has been upgraded to the latest version, which caused the file upload API to break. This change fixes the issue.
+
+The `ctx.request.files.file` in the new version is an array, so the code has been updated to pick the first one.
diff --git a/packages/core/src/routes/user-assets.ts b/packages/core/src/routes/user-assets.ts
index 9eb0c054597..19c155bccb1 100644
--- a/packages/core/src/routes/user-assets.ts
+++ b/packages/core/src/routes/user-assets.ts
@@ -52,13 +52,15 @@ export default function userAssetsRoutes<T extends ManagementApiRouter>(
     '/user-assets',
     koaGuard({
       files: object({
-        file: uploadFileGuard,
+        file: uploadFileGuard.array().min(1),
       }),
       response: userAssetsGuard,
     }),
     async (ctx, next) => {
-      const { file } = ctx.guard.files;
+      const { file: bodyFiles } = ctx.guard.files;
 
+      const file = bodyFiles[0];
+      assertThat(file, 'guard.invalid_input');
       assertThat(file.size <= maxUploadFileSize, 'guard.file_size_exceeded');
       assertThat(
         allowUploadMimeTypes.map(String).includes(file.mimetype),