diff --git a/packages/data-schemas/src/methods/file.spec.ts b/packages/data-schemas/src/methods/file.spec.ts
index 66fb44c761..1820a822c9 100644
--- a/packages/data-schemas/src/methods/file.spec.ts
+++ b/packages/data-schemas/src/methods/file.spec.ts
@@ -90,6 +90,23 @@ describe('File Methods', () => {
       expect(file?.expiresAt).toBeUndefined();
     });
 
+    it('casts string owner ids in atomic pipeline upserts', async () => {
+      const fileId = uuidv4();
+      const userId = new mongoose.Types.ObjectId();
+
+      const file = await fileMethods.createFile({
+        file_id: fileId,
+        user: userId.toString() as unknown as mongoose.Types.ObjectId,
+        filename: 'owned.txt',
+        filepath: '/uploads/owned.txt',
+        type: 'text/plain',
+        bytes: 100,
+      });
+
+      expect(file?.user).toEqual(userId);
+      await expect(File.countDocuments({ file_id: fileId, user: userId })).resolves.toBe(1);
+    });
+
     it('updates expiredAt monotonically with an atomic minimum', async () => {
       const fileId = uuidv4();
       const userId = new mongoose.Types.ObjectId();
diff --git a/packages/data-schemas/src/methods/file.ts b/packages/data-schemas/src/methods/file.ts
index 99563c0054..1f5b938095 100644
--- a/packages/data-schemas/src/methods/file.ts
+++ b/packages/data-schemas/src/methods/file.ts
@@ -368,6 +368,9 @@ export function createFileMethods(mongoose: typeof import('mongoose')): {
     const definedFields = Object.fromEntries(
       Object.entries(fields).filter(([, value]) => value !== undefined),
     );
+    if (definedFields.user != null) {
+      definedFields.user = File.schema.path('user').cast(definedFields.user);
+    }
     const insertDefaults = {
       object: { $ifNull: ['$object', 'file'] },
       usage: { $ifNull: ['$usage', 0] },