diff --git a/geomagio/algorithm/AverageAlgorithm.py b/geomagio/algorithm/AverageAlgorithm.py
index 3a0879188e913b51001840bc7b04ee8dd2661a6f..1787ad199d57f1930a4c614eee406287ac8d1a19 100644
--- a/geomagio/algorithm/AverageAlgorithm.py
+++ b/geomagio/algorithm/AverageAlgorithm.py
@@ -122,7 +122,7 @@ class AverageAlgorithm(Algorithm):
 
         self.outlocation = self.outlocation or timeseries[0].stats.location
 
-        self.min_count = self.min_count or len(timeseries)
+        self.min_count = self.min_count or len(self.observatories)
         self.min_count_start = self.min_count_start or timeseries[0].stats.starttime
         self.min_count_end = self.min_count_end or timeseries[0].stats.endtime