diff --git a/Localization/histogram_filter/histogram_filter.py b/Localization/histogram_filter/histogram_filter.py
index 8404646c..db715a6d 100644
--- a/Localization/histogram_filter/histogram_filter.py
+++ b/Localization/histogram_filter/histogram_filter.py
@@ -68,7 +68,7 @@ def calc_gaussian_observation_pdf(gmap, z, iz, ix, iy, std):
     # predicted range
     x = ix * gmap.xy_reso + gmap.minx
     y = iy * gmap.xy_reso + gmap.miny
-    d = math.sqrt((x - z[iz, 1]) ** 2 + (y - z[iz, 2]) ** 2)
+    d = math.hypot(x - z[iz, 1], y - z[iz, 2])
 
     # likelihood
     pdf = (1.0 - norm.cdf(abs(d - z[iz, 0]), 0.0, std))