diff --git a/data-gen/kubric/kubric/file_io.py b/data-gen/kubric/kubric/file_io.py
index 789d7d6..1d491c9 100644
--- a/data-gen/kubric/kubric/file_io.py
+++ b/data-gen/kubric/kubric/file_io.py
@@ -74,7 +74,11 @@ class _NumpyEncoder(json.JSONEncoder):
     def default(self, o):
         if isinstance(o, np.ndarray):
             return o.tolist()
-        return json.JSONEncoder.default(self, o)
+        elif isinstance(o, (np.floating,)):
+            return float(o)
+        elif isinstance(o, (np.integer,)):
+            return int(o)
+        return super().default(o)
 
 
 def write_png(data: np.array, filename: PathLike) -> None:
diff --git a/data-gen/kubric/kubric/renderer/blender.py b/data-gen/kubric/kubric/renderer/blender.py
index a9b2e28..9570343 100644
--- a/data-gen/kubric/kubric/renderer/blender.py
+++ b/data-gen/kubric/kubric/renderer/blender.py
@@ -189,6 +189,7 @@ def use_gpu(self) -> bool:
     def use_gpu(self, value: bool):
         self.blender_scene.cycles.device = "GPU" if value else "CPU"
         if value:
+            bpy.context.preferences.addons["cycles"].preferences.compute_device_type = "CUDA" # or "OPTIX"
             # call get_devices() to let Blender detect GPU devices
             bpy.context.preferences.addons["cycles"].preferences.get_devices()
             devices_used = [d.name for d in bpy.context.preferences.addons["cycles"].preferences.devices