diff --git a/lib/algorithm/kde.cpp b/lib/algorithm/kde.cpp
index 386a276..349656f 100644
--- a/lib/algorithm/kde.cpp
+++ b/lib/algorithm/kde.cpp
@@ -280,5 +280,5 @@ void gctl::kde2d::get_gradient_y_at(size_t m_id, const array<double> &mx,
 
 double gctl::kde2d::gaussian_kernel(double x, double y)
 {
-    return exp(-0.5*(x*x + y*y))/sqrt(2*M_PI);
+    return exp(-0.5*(x*x + y*y))/(2*M_PI);
 }
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