diff --git a/statime/src/filters/kalman.rs b/statime/src/filters/kalman.rs
index 8f9a047e1..e70463a77 100644
--- a/statime/src/filters/kalman.rs
+++ b/statime/src/filters/kalman.rs
@@ -123,7 +123,7 @@ struct MeasurementErrorEstimator {
 
 impl MeasurementErrorEstimator {
     fn mean(&self) -> f64 {
-        self.data.iter().take(self.fill).sum::<f64>() / (self.data.len() as f64)
+        self.data.iter().take(self.fill).sum::<f64>() / (self.fill as f64)
     }
 
     fn variance(&self) -> f64 {