diff --git a/src/dbus_fast/_private/unmarshaller.py b/src/dbus_fast/_private/unmarshaller.py
index d5181f5f..e6199b0a 100644
--- a/src/dbus_fast/_private/unmarshaller.py
+++ b/src/dbus_fast/_private/unmarshaller.py
@@ -750,24 +750,26 @@ def _read_body(self) -> None:
         flags = MESSAGE_FLAG_MAP.get(self._flag)
         if flags is None:
             flags = MESSAGE_FLAG_INTENUM(self._flag)
-        self._message = Message(
-            message_type=MESSAGE_TYPE_MAP[self._message_type],
-            flags=flags,
-            unix_fds=self._unix_fds,
-            signature=tree,
-            body=body,
-            serial=self._serial,
+        message = Message.__new__(Message)
+        message._fast_init(
+            header_fields[HEADER_DESTINATION_IDX],
+            header_fields[HEADER_PATH_IDX],
+            header_fields[HEADER_INTERFACE_IDX],
+            header_fields[HEADER_MEMBER_IDX],
+            MESSAGE_TYPE_MAP[self._message_type],
+            flags,
+            header_fields[HEADER_ERROR_NAME_IDX],
+            header_fields[HEADER_REPLY_SERIAL_IDX] or 0,
+            header_fields[HEADER_SENDER_IDX],
+            self._unix_fds,
+            tree,
+            body,
+            self._serial,
             # The D-Bus implementation already validates the message,
             # so we don't need to do it again.
-            validate=False,
-            destination=header_fields[HEADER_DESTINATION_IDX],
-            path=header_fields[HEADER_PATH_IDX],
-            interface=header_fields[HEADER_INTERFACE_IDX],
-            member=header_fields[HEADER_MEMBER_IDX],
-            reply_serial=header_fields[HEADER_REPLY_SERIAL_IDX],
-            error_name=header_fields[HEADER_ERROR_NAME_IDX],
-            sender=header_fields[HEADER_SENDER_IDX],
+            False,
         )
+        self._message = message
         self._read_complete = True
 
     def unmarshall(self) -> Optional[Message]:
diff --git a/src/dbus_fast/message.pxd b/src/dbus_fast/message.pxd
index 891c8ceb..e7a9e2f7 100644
--- a/src/dbus_fast/message.pxd
+++ b/src/dbus_fast/message.pxd
@@ -41,16 +41,34 @@ cdef class Message:
     cdef public object message_type
     cdef public object flags
     cdef public object error_name
-    cdef public object reply_serial
+    cdef public unsigned int reply_serial
     cdef public object sender
-    cdef public cython.list unix_fds
+    cdef public list unix_fds
     cdef public object signature
     cdef public object signature_tree
     cdef public object body
-    cdef public object serial
+    cdef public unsigned int serial
 
     @cython.locals(
         body_buffer=cython.bytearray,
         header_buffer=cython.bytearray
     )
     cpdef _marshall(self, object negotiate_unix_fd)
+
+    cdef _fast_init(
+        self,
+        object destination,
+        object path,
+        object interface,
+        object member,
+        object message_type,
+        object flags,
+        object error_name,
+        unsigned int reply_serial,
+        object sender,
+        list unix_fds,
+        object signature_tree,
+        object body,
+        unsigned int serial,
+        bint validate
+    )
diff --git a/src/dbus_fast/message.py b/src/dbus_fast/message.py
index bbc5276c..fb5cd042 100644
--- a/src/dbus_fast/message.py
+++ b/src/dbus_fast/message.py
@@ -34,6 +34,14 @@
 MESSAGE_TYPE_METHOD_CALL = MessageType.METHOD_CALL
 
 
+_int = int
+_str = str
+_bool = bool
+_MessageType = MessageType
+_MessageFlag = MessageFlag
+_list = list
+
+
 class Message:
     """A class for sending and receiving messages through the
     :class:`MessageBus <dbus_fast.message_bus.BaseMessageBus>` with the
@@ -114,27 +122,57 @@ def __init__(
         body: list[Any] = [],
         serial: Optional[int] = None,
         validate: bool = True,
+    ) -> None:
+        self._fast_init(
+            destination,
+            path,
+            interface,
+            member,
+            message_type,
+            flags if type(flags) is MESSAGE_FLAG else MESSAGE_FLAG(flags),
+            str(error_name.value) if type(error_name) is ErrorType else error_name,
+            reply_serial or 0,
+            sender,
+            unix_fds,
+            signature
+            if type(signature) is SignatureTree
+            else get_signature_tree(signature or ""),
+            body,
+            serial or 0,
+            validate,
+        )
+
+    def _fast_init(
+        self,
+        destination: Optional[_str],
+        path: Optional[_str],
+        interface: Optional[_str],
+        member: Optional[_str],
+        message_type: _MessageType,
+        flags: _MessageFlag,
+        error_name: Optional[_str],
+        reply_serial: _int,
+        sender: _str,
+        unix_fds: _list[int],
+        signature_tree: SignatureTree,
+        body: _list[Any],
+        serial: _int,
+        validate: _bool,
     ) -> None:
         self.destination = destination
         self.path = path
         self.interface = interface
         self.member = member
         self.message_type = message_type
-        self.flags = flags if type(flags) is MESSAGE_FLAG else MESSAGE_FLAG(flags)
-        self.error_name = (
-            str(error_name.value) if type(error_name) is ErrorType else error_name
-        )
-        self.reply_serial = reply_serial or 0
+        self.flags = flags
+        self.error_name = error_name
+        self.reply_serial = reply_serial
         self.sender = sender
         self.unix_fds = unix_fds
-        if type(signature) is SignatureTree:
-            self.signature = signature.signature
-            self.signature_tree = signature
-        else:
-            self.signature = signature or ""  # type: ignore[assignment]
-            self.signature_tree = get_signature_tree(signature or "")
+        self.signature = signature_tree.signature
+        self.signature_tree = signature_tree
         self.body = body
-        self.serial = serial or 0
+        self.serial = serial
 
         if not validate:
             return