diff --git a/server/storage/s3.js b/server/storage/s3.js
index b77f91b3..d8610abe 100644
--- a/server/storage/s3.js
+++ b/server/storage/s3.js
@@ -11,7 +11,7 @@ class S3Storage {
     const result = await s3
       .headObject({ Bucket: this.bucket, Key: id })
       .promise();
-    return result.ContentLength;
+    return Number(result.ContentLength);
   }
 
   getStream(id) {