diff --git a/pytomoatt/src_rec.py b/pytomoatt/src_rec.py
index 54219e2..7119619 100644
--- a/pytomoatt/src_rec.py
+++ b/pytomoatt/src_rec.py
@@ -1025,7 +1025,7 @@ def calc_azi_gap(az):
             sorted_az = np.sort(az)
             az_diffs = np.diff(np.concatenate((sorted_az, [sorted_az[0] + 360])))
             return np.max(az_diffs)
-        max_gap = self.rec_points.groupby('src_index').apply(lambda x: calc_azi_gap(x['az'].values))
+        max_gap = self.rec_points.groupby('src_index')['az'].apply(lambda x: calc_azi_gap(x.values))
         self.src_points = self.src_points[(max_gap < max_azi_gap)]     
         
         self.update()