diff --git a/core/src/services/gcs/core.rs b/core/src/services/gcs/core.rs
index b00c0e19cae1..86d73bc2e528 100644
--- a/core/src/services/gcs/core.rs
+++ b/core/src/services/gcs/core.rs
@@ -288,7 +288,7 @@ impl GcsCore {
                     "application/json; charset=UTF-8".parse().unwrap(),
                 )
                 .content(
-                    serde_json::to_string(&request_metadata)
+                    serde_json::to_vec(&request_metadata)
                         .expect("metadata serialization should success"),
                 );
             multipart = multipart.part(metadata_part);