diff --git a/system_property_chart.py b/system_property_chart.py
index 3ef6757d93514656c75843e189aa2e619fcaa107..8917d413f7f784dffd2691abbcfb504883b56e94 100644
--- a/system_property_chart.py
+++ b/system_property_chart.py
@@ -232,6 +232,8 @@ def register():
 
 
 def unregister():
+    Scene = bpy.types.Scene
+
     for cls in View3DEditProps, SequencerEditProps:
         delattr(Scene,
                 cls._PROP_STORAGE_ID,