diff --git a/stubs/pyserial/@tests/stubtest_allowlist.txt b/stubs/pyserial/@tests/stubtest_allowlist.txt
index 69717d5f7fd3..5a42b302756a 100644
--- a/stubs/pyserial/@tests/stubtest_allowlist.txt
+++ b/stubs/pyserial/@tests/stubtest_allowlist.txt
@@ -10,7 +10,6 @@ serial.serialjava  # No Java Communications API implementation found
 # but at runtime they are normal arguments that don't have consistent names.
 serial.serialutil.SerialBase.readinto
 serial.rfc2217.Serial.write
-serial.rs485.RS485.write
 serial.urlhandler.protocol_cp2110.Serial.write
 serial.urlhandler.protocol_loop.Serial.write
 serial.urlhandler.protocol_socket.Serial.write
diff --git a/stubs/pyserial/serial/rs485.pyi b/stubs/pyserial/serial/rs485.pyi
index b76617efb818..15b642b68b72 100644
--- a/stubs/pyserial/serial/rs485.pyi
+++ b/stubs/pyserial/serial/rs485.pyi
@@ -1,3 +1,5 @@
+from _typeshed import ReadableBuffer
+
 import serial
 
 class RS485Settings:
@@ -15,4 +17,5 @@ class RS485Settings:
         delay_before_rx: float | None = None,
     ) -> None: ...
 
-class RS485(serial.Serial): ...
+class RS485(serial.Serial):
+    def write(self, b: ReadableBuffer) -> None: ...
diff --git a/stubs/pyserial/serial/serialutil.pyi b/stubs/pyserial/serial/serialutil.pyi
index a21681d688e7..8d0464949db9 100644
--- a/stubs/pyserial/serial/serialutil.pyi
+++ b/stubs/pyserial/serial/serialutil.pyi
@@ -34,11 +34,11 @@ class Timeout:
     TIME: Callable[[], float]
     is_infinite: bool
     is_non_blocking: bool
-    duration: float
-    target_time: float
-    def __init__(self, duration: float) -> None: ...
+    duration: float | None
+    target_time: float | None
+    def __init__(self, duration: float | None) -> None: ...
     def expired(self) -> bool: ...
-    def time_left(self) -> float: ...
+    def time_left(self) -> float | None: ...
     def restart(self, duration: float) -> None: ...
 
 class SerialBase(io.RawIOBase):
diff --git a/stubs/pyserial/serial/threaded/__init__.pyi b/stubs/pyserial/serial/threaded/__init__.pyi
index 4cc3c15648ee..214ea0bbd45f 100644
--- a/stubs/pyserial/serial/threaded/__init__.pyi
+++ b/stubs/pyserial/serial/threaded/__init__.pyi
@@ -42,7 +42,8 @@ class ReaderThread(threading.Thread, Generic[_P]):
     protocol: _P
     def __init__(self, serial_instance: Serial, protocol_factory: Callable[[], _P]) -> None: ...
     def stop(self) -> None: ...
-    def write(self, data: ReadableBuffer) -> int: ...
+    # RS485.write discards the underlying byte count and returns None.
+    def write(self, data: ReadableBuffer) -> int | None: ...
     def close(self) -> None: ...
     def connect(self) -> tuple[Self, _P]: ...
     def __enter__(self) -> _P: ...