diff --git a/openflexure_microscope/api/default_extensions/__init__.py b/openflexure_microscope/api/default_extensions/__init__.py
index 1c080a93..6cbef3be 100644
--- a/openflexure_microscope/api/default_extensions/__init__.py
+++ b/openflexure_microscope/api/default_extensions/__init__.py
@@ -1,8 +1,10 @@
 import logging
 import traceback
 from contextlib import contextmanager
+from labthings.extensions import BaseExtension
+from typing import List, Type
 
-LABTHINGS_EXTENSIONS = []
+LABTHINGS_EXTENSIONS: List[Type[BaseExtension]] = []
 
 
 @contextmanager