diff --git a/openflexure_microscope/api/app.py b/openflexure_microscope/api/app.py
index be2d5b38..b37642a3 100644
--- a/openflexure_microscope/api/app.py
+++ b/openflexure_microscope/api/app.py
@@ -97,7 +97,7 @@ app, labthing = create_app(
 cors = CORS(app)
 
 # Use custom JSON encoder
-app.config['LABTHINGS_JSON_ENCODER'] = JSONEncoder
+labthing.json_encoder = JSONEncoder
 app.json_encoder = JSONEncoder
 
 # Attach lab devices