diff --git a/script/Devices/ImageStats.py b/script/Devices/ImageStats.py
index 754abce..4051b65 100644
--- a/script/Devices/ImageStats.py
+++ b/script/Devices/ImageStats.py
@@ -98,6 +98,7 @@ class ImageStats(DeviceBase):
         self.source = source
         self.com_x_samples, self.com_y_samples = [], []
         self.rms_x_samples, self.rms_y_samples = [], []
+        self.background = None
         class ComX(Readable):
             def read(self):     
                 if len(self.image_stats.com_x_samples)==0: return None