diff --git a/picamera_coverage.zip b/picamera_coverage.zip
index 7c9090de..121e8c33 100644
Binary files a/picamera_coverage.zip and b/picamera_coverage.zip differ
diff --git a/src/openflexure_microscope_server/things/autofocus.py b/src/openflexure_microscope_server/things/autofocus.py
index eebff335..695c349c 100644
--- a/src/openflexure_microscope_server/things/autofocus.py
+++ b/src/openflexure_microscope_server/things/autofocus.py
@@ -405,6 +405,7 @@ class AutofocusThing(lt.Thing):
     field of view to assess focus (autofocus and testing the success of a z-stack)
     """
 
+    _class_settings = {"validate_properties_on_set": True}
     _cam: BaseCamera = lt.thing_slot()
     _stage: BaseStage = lt.thing_slot()
 
diff --git a/src/openflexure_microscope_server/things/background_detect.py b/src/openflexure_microscope_server/things/background_detect.py
index c2753a75..fcf03b9d 100644
--- a/src/openflexure_microscope_server/things/background_detect.py
+++ b/src/openflexure_microscope_server/things/background_detect.py
@@ -38,6 +38,8 @@ class ChannelBlankError(lt.exceptions.InvocationError):
 class BackgroundDetectAlgorithm(lt.Thing):
     """The base class for defining background detect algorithms."""
 
+    _class_settings = {"validate_properties_on_set": True}
+
     display_name: str = lt.property(default="Base Detector", readonly=True)
 
     def __init__(self, thing_server_interface: lt.ThingServerInterface) -> None:
diff --git a/src/openflexure_microscope_server/things/camera/__init__.py b/src/openflexure_microscope_server/things/camera/__init__.py
index 96840889..b9f0f2a7 100644
--- a/src/openflexure_microscope_server/things/camera/__init__.py
+++ b/src/openflexure_microscope_server/things/camera/__init__.py
@@ -172,6 +172,8 @@ class BaseCamera(OFMThing):
     ``__init__`` method of the subclass.
     """
 
+    _class_settings = {"validate_properties_on_set": True}
+
     _all_background_detectors: Mapping[str, BackgroundDetectAlgorithm] = lt.thing_slot()
 
     mjpeg_stream = lt.outputs.MJPEGStreamDescriptor()
diff --git a/src/openflexure_microscope_server/things/camera_stage_mapping.py b/src/openflexure_microscope_server/things/camera_stage_mapping.py
index 813c762f..341683a9 100644
--- a/src/openflexure_microscope_server/things/camera_stage_mapping.py
+++ b/src/openflexure_microscope_server/things/camera_stage_mapping.py
@@ -119,6 +119,8 @@ class CameraStageMapper(lt.Thing):
     override the ``get_xyz_position()`` and ``move_to_xyz_position()`` methods.
     """
 
+    _class_settings = {"validate_properties_on_set": True}
+
     _cam: BaseCamera = lt.thing_slot()
     _stage: BaseStage = lt.thing_slot()
 
diff --git a/src/openflexure_microscope_server/things/illumination.py b/src/openflexure_microscope_server/things/illumination.py
index 2e444138..ce8647b0 100644
--- a/src/openflexure_microscope_server/things/illumination.py
+++ b/src/openflexure_microscope_server/things/illumination.py
@@ -12,6 +12,8 @@ from .stage.sangaboard import SangaboardThing
 class Illumination(lt.Thing):
     """Base class for an illumination controller."""
 
+    _class_settings = {"validate_properties_on_set": True}
+
     @lt.action
     def set_led(self, led_on: bool = True) -> None:
         """Set the LED to on or off."""
diff --git a/src/openflexure_microscope_server/things/scan_workflows.py b/src/openflexure_microscope_server/things/scan_workflows.py
index c92900c2..fe4ee898 100644
--- a/src/openflexure_microscope_server/things/scan_workflows.py
+++ b/src/openflexure_microscope_server/things/scan_workflows.py
@@ -62,6 +62,8 @@ class ScanWorkflow(Generic[SettingModelType], lt.Thing):
     scan planning, acquisition routine.
     """
 
+    _class_settings = {"validate_properties_on_set": True}
+
     display_name: str = lt.property(default="Base Workflow", readonly=True)
     ui_blurb: str = lt.property(
         default="If you see this message, something is wrong.", readonly=True
diff --git a/src/openflexure_microscope_server/things/smart_scan.py b/src/openflexure_microscope_server/things/smart_scan.py
index 5b2e54af..25b0a60b 100644
--- a/src/openflexure_microscope_server/things/smart_scan.py
+++ b/src/openflexure_microscope_server/things/smart_scan.py
@@ -119,6 +119,8 @@ class SmartScanThing(OFMThing):
     past scans.
     """
 
+    _class_settings = {"validate_properties_on_set": True}
+
     _cam: BaseCamera = lt.thing_slot()
     _stage: BaseStage = lt.thing_slot()
     _all_workflows: Mapping[str, ScanWorkflow] = lt.thing_slot()
diff --git a/src/openflexure_microscope_server/things/stage/__init__.py b/src/openflexure_microscope_server/things/stage/__init__.py
index d0bdeab6..e5b0b72b 100644
--- a/src/openflexure_microscope_server/things/stage/__init__.py
+++ b/src/openflexure_microscope_server/things/stage/__init__.py
@@ -106,6 +106,7 @@ class BaseStage(lt.Thing):
     """
 
     _axis_names = ("x", "y", "z")
+    _class_settings = {"validate_properties_on_set": True}
 
     def __init__(self, thing_server_interface: lt.ThingServerInterface) -> None:
         """Initialise the stage.
diff --git a/src/openflexure_microscope_server/things/stage_measure.py b/src/openflexure_microscope_server/things/stage_measure.py
index 411e57ed..4d426a51 100644
--- a/src/openflexure_microscope_server/things/stage_measure.py
+++ b/src/openflexure_microscope_server/things/stage_measure.py
@@ -117,6 +117,8 @@ class ParasiticMotionError(lt.exceptions.InvocationError):
 class RangeofMotionThing(lt.Thing):
     """A class used to measure the range of motion of the stage in X and Y."""
 
+    _class_settings = {"validate_properties_on_set": True}
+
     _autofocus: AutofocusThing = lt.thing_slot()
     _cam: BaseCamera = lt.thing_slot()
     _csm: CameraStageMapper = lt.thing_slot()
diff --git a/src/openflexure_microscope_server/things/system.py b/src/openflexure_microscope_server/things/system.py
index ff6a2fed..d1d02517 100644
--- a/src/openflexure_microscope_server/things/system.py
+++ b/src/openflexure_microscope_server/things/system.py
@@ -46,6 +46,8 @@ class OpenFlexureSystem(lt.Thing):
         of the system.
     """
 
+    _class_settings = {"validate_properties_on_set": True}
+
     _microscope_id: Optional[str] = None
 
     @lt.setting
diff --git a/tests/unit_tests/test_simulated_camera.py b/tests/unit_tests/test_simulated_camera.py
index 4935d9d6..dd499fc9 100644
--- a/tests/unit_tests/test_simulated_camera.py
+++ b/tests/unit_tests/test_simulated_camera.py
@@ -7,6 +7,7 @@ import numpy as np
 import pytest
 from hypothesis import given
 from hypothesis import strategies as st
+from pydantic import ValidationError
 
 import labthings_fastapi as lt
 
@@ -210,7 +211,7 @@ def test_objective_getter_setter(camera):
         camera.objective = 15
     with pytest.raises(ValueError, match=err_msg):
         camera.objective = 0
-    with pytest.raises(ValueError, match=err_msg):
+    with pytest.raises(ValidationError):
         camera.objective = "twenty"
 
 
diff --git a/tests/unit_tests/test_smart_scan.py b/tests/unit_tests/test_smart_scan.py
index e8abf2d5..566faea9 100644
--- a/tests/unit_tests/test_smart_scan.py
+++ b/tests/unit_tests/test_smart_scan.py
@@ -25,7 +25,7 @@ from unittest import mock
 
 import pytest
 from fastapi import HTTPException
-from pydantic import BaseModel
+from pydantic import BaseModel, ValidationError
 
 from labthings_fastapi.exceptions import InvocationCancelledError
 from labthings_fastapi.testing import create_thing_without_server
@@ -206,8 +206,11 @@ def test_setting_workflows(caplog, mocker):
     with caplog.at_level(logging.WARNING), smart_scan_thing:
         assert smart_scan_thing._workflow_name == "foo"
         assert smart_scan_thing._workflow is workflows["foo"]
-        # Can't set None, warns doesn't change
-        smart_scan_thing.workflow_name = None
+        # Can't set None, raises a ValidationError
+        with pytest.raises(ValidationError):
+            smart_scan_thing.workflow_name = None
+        # Empty string still won't change, but just warns
+        smart_scan_thing.workflow_name = ""
         assert len(caplog.records) == 1
         assert smart_scan_thing._workflow_name == "foo"
         assert smart_scan_thing._workflow is workflows["foo"]