diff --git a/src/dbus_fast/_private/marshaller.pxd b/src/dbus_fast/_private/marshaller.pxd
index f94c95d..54b23ea 100644
--- a/src/dbus_fast/_private/marshaller.pxd
+++ b/src/dbus_fast/_private/marshaller.pxd
@@ -33,14 +33,14 @@ cdef class Marshaller:
     )
     cdef unsigned int _write_boolean(self, object boolean)
 
-    cpdef write_string(self, str value, object _type)
+    cpdef write_string(self, object value, object _type)
 
     @cython.locals(
         value_len=cython.uint,
         signature_len=cython.uint,
         written=cython.uint,
     )
-    cdef unsigned int _write_string(self, str value)
+    cdef unsigned int _write_string(self, object value)
 
     @cython.locals(
         signature_len=cython.uint,
diff --git a/src/dbus_fast/_private/marshaller.py b/src/dbus_fast/_private/marshaller.py
index cdf45b2..9a9bff8 100644
--- a/src/dbus_fast/_private/marshaller.py
+++ b/src/dbus_fast/_private/marshaller.py
@@ -179,18 +179,18 @@ class Marshaller:
     def _marshall(self) -> bytearray:
         """Marshalls the body into a byte array"""
         try:
-            self._construct_buffer()
+            return self._construct_buffer()
         except KeyError as ex:
             raise NotImplementedError(f'type is not implemented yet: "{ex.args}"')
         except error:
             self.signature_tree.verify(self.body)
-        return self._buf
 
-    def _construct_buffer(self) -> None:
+    def _construct_buffer(self) -> bytearray:
         self._buf.clear()
         body = self.body
         for i, type_ in enumerate(self.signature_tree.types):
             self._write_single(type_, body[i])
+        return self._buf
 
     _writers: Dict[
         str,
diff --git a/tests/test_marshaller.py b/tests/test_marshaller.py
index c2af741..290f5f3 100644
--- a/tests/test_marshaller.py
+++ b/tests/test_marshaller.py
@@ -1,8 +1,8 @@
 import io
 import json
 import os
+from enum import Enum
 from typing import Any, Dict
-from unittest.mock import patch
 
 import pytest
 
@@ -566,3 +566,24 @@ def test_unmarshall_big_endian_message():
     message = unmarshaller.message
     unpacked = unpack_variants(message.body)
     assert unpacked == [42, "zip", "Trusted", True]
+
+
+class RaucState(str, Enum):
+    """Rauc slot states."""
+
+    GOOD = "good"
+    BAD = "bad"
+    ACTIVE = "active"
+
+
+def test_marshalling_enum():
+    """Test marshalling an enum."""
+    msg = Message(
+        path="/test",
+        member="test",
+        signature="s",
+        body=[RaucState.GOOD],
+    )
+    marshalled = msg._marshall(False)
+    unmarshalled_msg = Unmarshaller(io.BytesIO(marshalled)).unmarshall()
+    assert unpack_variants(unmarshalled_msg.body)[0] == RaucState.GOOD.value