diff --git a/betterproto-extras/src/merging.rs b/betterproto-extras/src/merging.rs
index 683f5f0..5738bb1 100644
--- a/betterproto-extras/src/merging.rs
+++ b/betterproto-extras/src/merging.rs
@@ -3,7 +3,7 @@ use crate::{
     py_any_extras::PyAnyExtras,
 };
 use prost_reflect::{DynamicMessage, Value};
-use pyo3::{PyAny, PyObject, ToPyObject};
+use pyo3::{PyAny, PyObject, ToPyObject, types::PyBytes};
 
 pub fn merge_msg_into_pyobj(obj: &PyAny, mut msg: DynamicMessage) -> Result<()> {
     for field in msg.take_fields() {
@@ -22,7 +22,7 @@ pub fn merge_msg_into_pyobj(obj: &PyAny, mut msg: DynamicMessage) -> Result<()>
     if !buf.is_empty() {
         let mut unknown_fields = obj.getattr("_unknown_fields")?.extract::<Vec<u8>>()?;
         unknown_fields.append(&mut buf);
-        obj.setattr("_unknown_fields", unknown_fields)?;
+        obj.setattr("_unknown_fields", PyBytes::new(obj.py(), &unknown_fields))?;
     }
 
     obj.setattr("_serialized_on_wire", true)?;