diff --git a/NumLib/Function/LinearInterpolationOnSurface.cpp b/NumLib/Function/LinearInterpolationOnSurface.cpp
index f5fd90ee7cacf80a8227a22a262dc8a1fc6beaf6..f463e80959e55865c6c97467d2d408c528f545b2 100644
--- a/NumLib/Function/LinearInterpolationOnSurface.cpp
+++ b/NumLib/Function/LinearInterpolationOnSurface.cpp
@@ -62,7 +62,10 @@ double LinearInterpolationOnSurface::operator()(const MathLib::Point3d& pnt) con
 	return val;
 }
 
-double LinearInterpolationOnSurface::interpolateInTri(const GeoLib::Triangle &tri, double const* const vertex_values, double const* const pnt) const
+double LinearInterpolationOnSurface::interpolateInTri(
+	const GeoLib::Triangle &tri,
+	double const* const vertex_values,
+	MathLib::Point3d const& pnt) const
 {
 	std::vector<GeoLib::Point> pnts;
 	for (unsigned i=0; i<3; i++)
diff --git a/NumLib/Function/LinearInterpolationOnSurface.h b/NumLib/Function/LinearInterpolationOnSurface.h
index f40f0e1a3a6506a5134d31b22edaa31fd7e6e023..b77ca7c7bed081000b9e7b4c4ea55a24e568e867 100644
--- a/NumLib/Function/LinearInterpolationOnSurface.h
+++ b/NumLib/Function/LinearInterpolationOnSurface.h
@@ -81,7 +81,9 @@ private:
 	 * @param pnt
 	 * @return
 	 */
-	double interpolateInTri(const GeoLib::Triangle &tri, double const* const vertex_values, double const* const pnt) const;
+	double interpolateInTri(const GeoLib::Triangle &tri,
+		double const* const vertex_values,
+		MathLib::Point3d const& pnt) const;
 
 	/// a surface object
 	const GeoLib::Surface& _sfc;