diff --git a/openflexure_microscope/microscope.py b/openflexure_microscope/microscope.py
index e24a60be..b3c29997 100644
--- a/openflexure_microscope/microscope.py
+++ b/openflexure_microscope/microscope.py
@@ -48,7 +48,7 @@ class Microscope:
 
         # Initialise with an empty composite lock
         #: :py:class:`labthings.CompositeLock`: Composite lock for locking both camera and stage
-        self.lock: Union[CompositeLock, StrictLock] = CompositeLock([])
+        self.lock: CompositeLock = CompositeLock([])
 
         self.camera: BaseCamera = None  #: Currently connected camera object
         self.stage: BaseStage = None  #: Currently connected stage object