diff --git a/pymodbus/transport/transport.py b/pymodbus/transport/transport.py
index be9b32cca1..b9a98da2e9 100644
--- a/pymodbus/transport/transport.py
+++ b/pymodbus/transport/transport.py
@@ -156,10 +156,10 @@ def __init__(
         self.is_server = is_server
         self.is_closing = False
 
-        self.transport: asyncio.BaseTransport = None
-        self.loop: asyncio.AbstractEventLoop = None
+        self.transport: asyncio.BaseTransport = None  # type: ignore[assignment]
+        self.loop: asyncio.AbstractEventLoop = None  # type: ignore[assignment]
         self.recv_buffer: bytes = b""
-        self.call_create: Callable[[], Coroutine[Any, Any, Any]] = lambda: None
+        self.call_create: Callable[[], Coroutine[Any, Any, Any]] = lambda: None  # type: ignore[assignment, return-value]
         if self.is_server:
             self.active_connections: dict[str, ModbusProtocol] = {}
         else:
@@ -415,7 +415,7 @@ def transport_close(self, intern: bool = False, reconnect: bool = False) -> None
             if hasattr(self.transport, "abort"):
                 self.transport.abort()
             self.transport.close()
-            self.transport = None
+            self.transport = None  # type: ignore[assignment]
         self.recv_buffer = b""
         if self.is_server:
             for _key, value in self.active_connections.items():
diff --git a/pymodbus/transport/transport_serial.py b/pymodbus/transport/transport_serial.py
index 63c1affa5a..017c3687f7 100644
--- a/pymodbus/transport/transport_serial.py
+++ b/pymodbus/transport/transport_serial.py
@@ -51,7 +51,7 @@ def close(self, exc: Exception | None = None) -> None:
         else:
             self.async_loop.remove_reader(self.sync_serial.fileno())
         self.sync_serial.close()
-        self.sync_serial = None
+        self.sync_serial = None  # type: ignore[assignment]
         if exc:
             with contextlib.suppress(Exception):
                 self._protocol.connection_lost(exc)
diff --git a/pyproject.toml b/pyproject.toml
index b781014c6a..c064943316 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -189,7 +189,7 @@ overgeneral-exceptions = "builtins.Exception"
 bad-functions = "map,input"
 
 [tool.mypy]
-strict_optional = false
+strict_optional = true
 show_error_codes = true
 local_partial_types = true
 strict_equality = true