diff --git a/DoubleDoubleGeometry/Geometry3D/Ellipse3D.cs b/DoubleDoubleGeometry/Geometry3D/Ellipse3D.cs
index c071118..28aa3e5 100644
--- a/DoubleDoubleGeometry/Geometry3D/Ellipse3D.cs
+++ b/DoubleDoubleGeometry/Geometry3D/Ellipse3D.cs
@@ -310,7 +310,7 @@ public override int GetHashCode() {
         }
 
         // A x^2 + B y^2 + C z^2 + D x y + E x z + F y z + G = 0
-        public class EllipseImplicitParameter {
+        private class EllipseImplicitParameter {
             public readonly ddouble A, B, C, D, E, F, G;
 
             public EllipseImplicitParameter(Vector2D axis, Quaternion rotation) {
diff --git a/DoubleDoubleGeometryTest/Geometry3D/Ellipse3DTests.cs b/DoubleDoubleGeometryTest/Geometry3D/Ellipse3DTests.cs
index e493734..53b3eff 100644
--- a/DoubleDoubleGeometryTest/Geometry3D/Ellipse3DTests.cs
+++ b/DoubleDoubleGeometryTest/Geometry3D/Ellipse3DTests.cs
@@ -10,8 +10,6 @@ public class Ellipse3DTests {
         public void Ellipse3DTest() {
             Ellipse3D ellipse = new((1, 2, 7), (4, 3), Vector3D.Rot((0, 0, 1), (2, 3, 4)));
 
-            Ellipse3D.EllipseImplicitParameter param = new Ellipse3D.EllipseImplicitParameter(ellipse.Axis, ellipse.Rotation);
-
             Vector3DAssert.AreEqual((1, 2, 7), ellipse.Center, 1e-30);
             Vector3DAssert.AreEqual(new Vector3D(2, 3, 4).Normal, ellipse.Normal, 1e-30);
             Assert.AreEqual(4d, ellipse.MajorAxis);