Fix typo

src/geomtools/powder/powdersum.py

@@ -236,7 +236,7 @@ class ImageAgg:
         self._ds_std[i] = self.deviation
         self._ds_count[i] = self.count
         self._ds_nfrm[i] = self.num_frames
-        self._ds_mask[i] = ~self.mask | (self.count == 0)
+        self._ds_mask[i] = ~self.mask[i] | (self.count == 0)
 
     def _send(self):
         self._comm.Gatherv(self._ds_mean, None, root=0)