diff --git a/robotoff/app/api.py b/robotoff/app/api.py
index 8c187a5b83..11e27bb479 100644
--- a/robotoff/app/api.py
+++ b/robotoff/app/api.py
@@ -895,7 +895,8 @@ def on_get(self, req: falcon.Request, resp: falcon.Response):
             result = model.detect_from_image(image, output_image=output_image)
 
             if output_image:
-                image_response(result.boxed_image, resp)
+                boxed_image = cast(Image.Image, result.boxed_image)
+                image_response(boxed_image, resp)
                 return
             else:
                 predictions[model_name] = result.to_json()