diff --git a/app/(chat)/api/chat/_lib/image-media.ts b/app/(chat)/api/chat/_lib/image-media.ts
index 91e42e09a..88532221a 100644
--- a/app/(chat)/api/chat/_lib/image-media.ts
+++ b/app/(chat)/api/chat/_lib/image-media.ts
@@ -611,7 +611,7 @@ export async function convertMessagesWithImages(
 
       const candidateImageUrl =
         part.type === "file"
-          ? part.url || part.data
+          ? part.url || (part as { data?: string | undefined }).data
           : part.type === "image"
             ? part.image || part.url
             : part.type === "image_url"