diff --git a/src/dbus_fast/_private/marshaller.pxd b/src/dbus_fast/_private/marshaller.pxd
index 958b8920..3a8f2642 100644
--- a/src/dbus_fast/_private/marshaller.pxd
+++ b/src/dbus_fast/_private/marshaller.pxd
@@ -15,19 +15,28 @@ cdef class Marshaller:
     cdef bytearray _buf
     cdef object body
 
-    cpdef unsigned int align(self, unsigned int n)
+    cpdef align(self, unsigned int n)
 
     @cython.locals(
         offset=cython.ulong,
     )
     cdef unsigned int _align(self, unsigned int n)
 
+    cpdef write_boolean(self, object boolean, object _type)
+
+    @cython.locals(
+        written=cython.uint,
+    )
+    cdef unsigned int _write_boolean(self, object boolean)
+
+    cpdef write_string(self, str value, object _type)
+
     @cython.locals(
         value_len=cython.uint,
         signature_len=cython.uint,
         written=cython.uint,
     )
-    cpdef write_string(self, str value, object _type)
+    cdef unsigned int _write_string(self, str value)
 
     @cython.locals(
         signature_len=cython.uint,
@@ -57,12 +66,14 @@ cdef class Marshaller:
     )
     cdef unsigned int _write_struct(self, object array, object type)
 
+    cpdef write_variant(self, object variant, object type)
+
     @cython.locals(
         written=cython.uint,
         signature=cython.str,
         signature_bytes=cython.bytes,
     )
-    cpdef write_variant(self, object variant, object type)
+    cdef unsigned int _write_variant(self, object variant, object type)
 
     @cython.locals(
         written=cython.uint,
diff --git a/src/dbus_fast/_private/marshaller.py b/src/dbus_fast/_private/marshaller.py
index abd886d1..42dfa89c 100644
--- a/src/dbus_fast/_private/marshaller.py
+++ b/src/dbus_fast/_private/marshaller.py
@@ -36,6 +36,9 @@ def _align(self, n):
         return offset
 
     def write_boolean(self, boolean: bool, type_: SignatureType) -> int:
+        return self._write_boolean(boolean)
+
+    def _write_boolean(self, boolean: bool) -> int:
         written = self._align(4)
         self._buf += PACKED_BOOL_TRUE if boolean else PACKED_BOOL_FALSE
         return written + 4
@@ -47,23 +50,29 @@ def _write_signature(self, signature_bytes) -> int:
         signature_len = len(signature_bytes)
         buf = self._buf
         buf.append(signature_len)
-        buf.extend(signature_bytes)
+        buf += signature_bytes
         buf.append(0)
         return signature_len + 2
 
     def write_string(self, value, type_: SignatureType) -> int:
+        return self._write_string(value)
+
+    def _write_string(self, value) -> int:
         value_bytes = value.encode()
         value_len = len(value)
         written = self._align(4) + 4
         buf = self._buf
-        buf.extend(PACK_UINT32(value_len))
-        buf.extend(value_bytes)
+        buf += PACK_UINT32(value_len)
+        buf += value_bytes
         written += value_len
         buf.append(0)
         written += 1
         return written
 
     def write_variant(self, variant: Variant, type_: SignatureType) -> int:
+        return self._write_variant(variant, type_)
+
+    def _write_variant(self, variant: Variant, type_: SignatureType) -> int:
         signature = variant.signature
         signature_bytes = signature.encode()
         written = self._write_signature(signature_bytes)
@@ -84,7 +93,7 @@ def _write_array(
         buf = self._buf
         offset = len(buf)
         written += self._align(4) + 4
-        buf.extend(PACKED_UINT32_ZERO)
+        buf += PACKED_UINT32_ZERO
         child_type = type_.children[0]
         token = child_type.token
 
@@ -98,7 +107,7 @@ def _write_array(
                 array_len += self.write_dict_entry([key, value], child_type)
         elif token == "y":
             array_len = len(array)
-            buf.extend(array)
+            buf += array
         elif token == "(":
             for value in array:
                 array_len += self._write_struct(value, child_type)
@@ -107,7 +116,7 @@ def _write_array(
             if not writer:
                 for value in array:
                     array_len += self._align(size) + size
-                    buf.extend(packer(value))  # type: ignore[misc]
+                    buf += packer(value)  # type: ignore[misc]
             else:
                 for value in array:
                     array_len += writer(self, value, child_type)
@@ -135,12 +144,28 @@ def write_dict_entry(self, dict_entry: List[Any], type_: SignatureType) -> int:
 
     def _write_single(self, type_: SignatureType, body: Any) -> int:
         t = type_.token
-        writer, packer, size = self._writers[t]
-        if not writer:
-            written = self._align(size)
-            self._buf.extend(packer(body))  # type: ignore[misc]
-            return written + size
-        return writer(self, body, type_)
+        if t == "y":
+            self._buf.append(body)
+            return 1
+        elif t == "u":
+            written = self._align(4)
+            self._buf += PACK_UINT32(body)
+            return written + 4
+        elif t == "a":
+            return self._write_array(body, type_)
+        elif t == "s" or t == "o":
+            return self._write_string(body)
+        elif t == "v":
+            return self._write_variant(body, type_)
+        elif t == "b":
+            return self._write_boolean(body)
+        else:
+            writer, packer, size = self._writers[t]
+            if not writer:
+                written = self._align(size)
+                self._buf += packer(body)  # type: ignore[misc]
+                return written + size
+            return writer(self, body, type_)
 
     def marshall(self) -> bytearray:
         """Marshalls the body into a byte array"""
@@ -154,26 +179,9 @@ def marshall(self) -> bytearray:
 
     def _construct_buffer(self) -> None:
         self._buf.clear()
-        writers = self._writers
         body = self.body
-        buf = self._buf
         for i, type_ in enumerate(self.signature_tree.types):
-            t = type_.token
-            if t == "y":
-                buf.append(body[i])
-            elif t == "u":
-                self._align(4)
-                buf.extend(PACK_UINT32(body[i]))
-            elif t == "a":
-                self._write_array(body[i], type_)
-            else:
-                writer, packer, size = writers[t]
-                if not writer:
-                    if size != 1:
-                        self._align(size)
-                    buf.extend(packer(body[i]))  # type: ignore[misc]
-                else:
-                    writer(self, body[i], type_)
+            self._write_single(type_, body[i])
 
     _writers: Dict[
         str,