diff --git a/openflexure_microscope/api/app.py b/openflexure_microscope/api/app.py
index 61112ad0..b603b666 100644
--- a/openflexure_microscope/api/app.py
+++ b/openflexure_microscope/api/app.py
@@ -92,6 +92,7 @@ app, labthing = create_app(
 cors = CORS(app)
 
 # Use custom JSON encoder
+app.config['LABTHINGS_JSON_ENCODER'] = JSONEncoder
 app.json_encoder = JSONEncoder
 
 # Attach lab devices