diff --git a/qcodes_contrib_drivers/drivers/Thorlabs/KDC101.py b/qcodes_contrib_drivers/drivers/Thorlabs/KDC101.py
index e78ddf9e7..91dedf4e6 100644
--- a/qcodes_contrib_drivers/drivers/Thorlabs/KDC101.py
+++ b/qcodes_contrib_drivers/drivers/Thorlabs/KDC101.py
@@ -37,6 +37,6 @@ def __init__(self,
             self._dll_path = dll_path
         else:
             self._dll_path = 'Thorlabs.MotionControl.KCube.DCServo.dll'
-        self._dll_dir: str | None = dll_dir if dll_dir else None
+        self._dll_dir: Optional[str] = dll_dir if dll_dir else None
         super().__init__(name, serial_number, self._dll_path, self._dll_dir,
                          simulation, polling, home, **kwargs)
diff --git a/qcodes_contrib_drivers/drivers/Thorlabs/KLS1550.py b/qcodes_contrib_drivers/drivers/Thorlabs/KLS1550.py
index 8fc71f88f..2c42de72a 100644
--- a/qcodes_contrib_drivers/drivers/Thorlabs/KLS1550.py
+++ b/qcodes_contrib_drivers/drivers/Thorlabs/KLS1550.py
@@ -34,6 +34,6 @@ def __init__(self,
             self._dll_path = dll_path
         else:
             self._dll_path = 'Thorlabs.MotionControl.KCube.LaserSource.dll'
-        self._dll_dir: str | None = dll_dir if dll_dir else None
+        self._dll_dir: Optional[str] = dll_dir if dll_dir else None
         super().__init__(name, serial_number, self._dll_path, self._dll_dir,
                          simulation, polling, **kwargs)
diff --git a/qcodes_contrib_drivers/drivers/Thorlabs/TDC001.py b/qcodes_contrib_drivers/drivers/Thorlabs/TDC001.py
index 200964200..dcba4a894 100644
--- a/qcodes_contrib_drivers/drivers/Thorlabs/TDC001.py
+++ b/qcodes_contrib_drivers/drivers/Thorlabs/TDC001.py
@@ -38,6 +38,6 @@ def __init__(self,
             self._dll_path = dll_path
         else:
             self._dll_path = 'Thorlabs.MotionControl.TCube.DCServo.dll'
-            self._dll_dir: str | None = dll_dir if dll_dir else None
+            self._dll_dir: Optional[str] = dll_dir if dll_dir else None
         super().__init__(name, serial_number, self._dll_path, self._dll_dir,
                          simulation, polling, home, **kwargs)
diff --git a/qcodes_contrib_drivers/drivers/Thorlabs/private/kinesis.py b/qcodes_contrib_drivers/drivers/Thorlabs/private/kinesis.py
index 22a07f8a2..06eff4ebc 100644
--- a/qcodes_contrib_drivers/drivers/Thorlabs/private/kinesis.py
+++ b/qcodes_contrib_drivers/drivers/Thorlabs/private/kinesis.py
@@ -33,7 +33,7 @@ def __init__(self,
         self.serial_number = serial_number
         self._serial_number = ctypes.c_char_p(self.serial_number.encode('ascii'))
         self._dll_path = dll_path
-        self._dll_dir: str | None = dll_dir if dll_dir else r'C:\Program Files\Thorlabs\Kinesis'
+        self._dll_dir: Optional[str] = dll_dir if dll_dir else r'C:\Program Files\Thorlabs\Kinesis'
         if sys.platform != 'win32':
             self._dll: Any = None
             raise OSError('Thorlabs Kinesis only works on Windows')