diff --git a/src/openflexure_microscope_server/server/__init__.py b/src/openflexure_microscope_server/server/__init__.py
index 137863bb..754a7799 100644
--- a/src/openflexure_microscope_server/server/__init__.py
+++ b/src/openflexure_microscope_server/server/__init__.py
@@ -72,9 +72,9 @@ def set_shutdown_function(shutdown_function: Callable[[], None]) -> None:
 
 
 def customise_server(
-    server: lt.ThingServer, application_config: OFMApplicationData
+    server: lt.ThingServer, application_config: OFMApplicationData, debug: bool = False
 ) -> None:
-    """Customise the server with additional endpoints, etc."""
+    """Customise the server with additional endpoints, debug mode etc."""
     if DEVELOPER_MODE:
         # Allow CORS in developer mode for easier testing with the webapp
         server.app.add_middleware(
@@ -88,6 +88,10 @@ def customise_server(
     add_v2_endpoints(server)
     add_static_files(server.app, application_config.data_folder)
 
+    # Configure logging to DEBUG if requested in CLI args.
+    if debug:
+        lt.logs.configure_thing_logger(logging.DEBUG)
+
     # Add an endpoint to get the logs - (directly calling the FastAPI decorator)
     server.app.get("/log/")(retrieve_log)
     server.app.get("/logfile/")(retrieve_log_from_file)
@@ -114,7 +118,8 @@ def serve_from_cli(argv: Optional[list[str]] = None) -> None:
         configure_logging(application_config.log_folder)
 
         server = lt.ThingServer.from_config(lt_config)
-        customise_server(server, application_config)
+        debug = bool(args.debug)
+        customise_server(server, application_config, debug)
 
         def shutdown_call() -> None:
             try:
diff --git a/tests/unit_tests/test_server_cli.py b/tests/unit_tests/test_server_cli.py
index 8f37e412..4c71a1c3 100644
--- a/tests/unit_tests/test_server_cli.py
+++ b/tests/unit_tests/test_server_cli.py
@@ -108,3 +108,39 @@ def test_failed_customise(mocker):
     assert isinstance(fallback_app, FastAPI)
     # An that it has the error to display
     assert str(fallback_app._context.error) == "Can't touch this"
+
+
+def test_debug_mode(mocker):
+    """Test that --debug flag triggers lt.logs.configure_thing_logger."""
+    # Mock the LabThings function that returns the server
+    mocker.patch(
+        "openflexure_microscope_server.server.lt.ThingServer.from_config",
+        return_value=mocker.Mock(),
+    )
+    # Mock customisation dependencies to avoid side effects
+    mocker.patch.object(ofm_server, "add_v2_endpoints")
+    mocker.patch.object(ofm_server, "add_static_files")
+    # Mock logging to avoid side effects and allow checking calls
+    mocker.patch.object(ofm_server, "configure_logging")
+    mocker.patch.object(ofm_server, "retrieve_log")
+    mocker.patch.object(ofm_server, "retrieve_log_from_file")
+    # Mock uvicorn.run to avoid starting a server
+    mocker.patch("openflexure_microscope_server.server.uvicorn.run")
+
+    # Mock the target function
+    mock_configure_thing_logger = mocker.patch(
+        "openflexure_microscope_server.server.lt.logs.configure_thing_logger"
+    )
+
+    # 1. Run with --debug
+    ofm_server.serve_from_cli(["-c", SIM_CONFIG, "--debug"])
+
+    # Verify it was called with DEBUG level
+    mock_configure_thing_logger.assert_called_once_with(logging.DEBUG)
+
+    # 2. Run without --debug
+    mock_configure_thing_logger.reset_mock()
+    ofm_server.serve_from_cli(["-c", SIM_CONFIG])
+
+    # Verify it was NOT called
+    mock_configure_thing_logger.assert_not_called()