diff --git a/libs/geom/include/psemek/geom/math.hpp b/libs/geom/include/psemek/geom/math.hpp
index 61f91c44..81586461 100644
--- a/libs/geom/include/psemek/geom/math.hpp
+++ b/libs/geom/include/psemek/geom/math.hpp
@@ -57,6 +57,15 @@ namespace psemek::geom
 		return std::sin(x) / x;
 	}
 
+	template <typename T>
+	T acos_over_sqrt_1_minus_x2(T const & x)
+	{
+		auto t = std::sqrt(T{1} - x * x);
+		if (t < std::numeric_limits<T>::epsilon())
+			return T{1};
+		return std::acos(x) / t;
+	}
+
 	namespace detail
 	{