diff --git a/packages/core/src/harness/harness.ts b/packages/core/src/harness/harness.ts
index a9fef33026d..cbf924cde43 100644
--- a/packages/core/src/harness/harness.ts
+++ b/packages/core/src/harness/harness.ts
@@ -1239,7 +1239,7 @@ export class Harness<TState extends HarnessStateSchema = HarnessStateSchema> {
           return {
             type: 'file' as const,
             data: f.data,
-            mimeType: f.mediaType,
+            mediaType: f.mediaType,
             filename: f.filename,
           };
         });