Index: Core/Common/src/Core.Common.Base/Geometry/Math2D.cs
===================================================================
diff -u -rf28fac2f7d391c4d48691c180f7ae8335b278c72 -re678af24e939bdb6b49294b16b06af9565bef9b1
--- Core/Common/src/Core.Common.Base/Geometry/Math2D.cs	(.../Math2D.cs)	(revision f28fac2f7d391c4d48691c180f7ae8335b278c72)
+++ Core/Common/src/Core.Common.Base/Geometry/Math2D.cs	(.../Math2D.cs)	(revision e678af24e939bdb6b49294b16b06af9565bef9b1)
@@ -92,6 +92,33 @@
         }
 
         /// <summary>
+        /// Creates an enumerator that converts a sequence of line points to a sequence of line segments 
+        /// and adds a segment between the last and the first point of the sequence.
+        /// </summary>
+        /// <param name="linePoints">The line points.</param>
+        /// <returns>A sequence of N elements, where N is the number of elements in <paramref name="linePoints"/>,
+        /// or 0 if <paramref name="linePoints"/> has one or no elements.</returns>
+        public static IEnumerable<Segment2D> ConvertLinePointsToClosingLineSegments(IEnumerable<Point2D> linePoints)
+        {
+            if (linePoints.Count() < 2)
+            {
+                yield break;
+            }
+
+            Point2D endPoint = linePoints.Last();
+            foreach (Point2D linePoint in linePoints)
+            {
+                Point2D startPoint = endPoint;
+                endPoint = linePoint;
+
+                if (startPoint != null)
+                {
+                    yield return new Segment2D(startPoint, endPoint);
+                }
+            }
+        }
+
+        /// <summary>
         /// Determines the intersection point of a line which passes through the <paramref name="line1Point1"/> and 
         /// the <paramref name="line1Point2"/>; and a line which passes through the <paramref name="line2Point1"/>
         /// and the <paramref name="line2Point2"/>.
Index: Core/Common/test/Core.Common.Base.Test/Geometry/Math2DTest.cs
===================================================================
diff -u -rb513e76d805898795483251f7d070489dfd20b9b -re678af24e939bdb6b49294b16b06af9565bef9b1
--- Core/Common/test/Core.Common.Base.Test/Geometry/Math2DTest.cs	(.../Math2DTest.cs)	(revision b513e76d805898795483251f7d070489dfd20b9b)
+++ Core/Common/test/Core.Common.Base.Test/Geometry/Math2DTest.cs	(.../Math2DTest.cs)	(revision e678af24e939bdb6b49294b16b06af9565bef9b1)
@@ -203,6 +203,46 @@
         [Test]
         [TestCase(0)]
         [TestCase(1)]
+        public void ConvertLinePointsToClosingLineSegments_TooFewPoints_ReturnEmpty(int pointCount)
+        {
+            // Setup
+            IEnumerable<Point2D> linePoints = Enumerable.Repeat(new Point2D(0, 0), pointCount);
+
+            // Call
+            IEnumerable<Segment2D> segments = Math2D.ConvertLinePointsToClosingLineSegments(linePoints);
+
+            // Assert
+            CollectionAssert.IsEmpty(segments);
+        }
+
+        [Test]
+        public void ConvertLinePointsToClosingLineSegments_TwoPoints_ReturnsExpectedSegments()
+        {
+            // Setup
+            var linePoints = new[]
+            {
+                new Point2D(0, 0),
+                new Point2D(1, 1)
+            };
+
+            // Call
+            Segment2D[] segments = Math2D.ConvertLinePointsToClosingLineSegments(linePoints).ToArray();
+
+            // Assert
+            Assert.AreEqual(2, segments.Length);
+
+            Segment2D firstSegment = segments[0];
+            Assert.AreEqual(linePoints[1], firstSegment.FirstPoint);
+            Assert.AreEqual(linePoints[0], firstSegment.SecondPoint);
+
+            Segment2D secondSegment = segments[1];
+            Assert.AreEqual(linePoints[0], secondSegment.FirstPoint);
+            Assert.AreEqual(linePoints[1], secondSegment.SecondPoint);
+        }
+
+        [Test]
+        [TestCase(0)]
+        [TestCase(1)]
         public void SplitLineAtLengths_TooFewPoints_ThrowArgumentException(int pointCount)
         {
             // Setup
Index: Ringtoets/MacroStabilityInwards/src/Ringtoets.MacroStabilityInwards.Service/MacroStabilityInwardsInputValidator.cs
===================================================================
diff -u -r73bd43678d003eca592c2ce14a2500a983d9b4c9 -re678af24e939bdb6b49294b16b06af9565bef9b1
--- Ringtoets/MacroStabilityInwards/src/Ringtoets.MacroStabilityInwards.Service/MacroStabilityInwardsInputValidator.cs	(.../MacroStabilityInwardsInputValidator.cs)	(revision 73bd43678d003eca592c2ce14a2500a983d9b4c9)
+++ Ringtoets/MacroStabilityInwards/src/Ringtoets.MacroStabilityInwards.Service/MacroStabilityInwardsInputValidator.cs	(.../MacroStabilityInwardsInputValidator.cs)	(revision e678af24e939bdb6b49294b16b06af9565bef9b1)
@@ -147,7 +147,7 @@
             {
                 bool isNear = soilProfile2D.Layers.Any(l => IsPointNearSoilSegments(
                                                            surfaceLinePoint,
-                                                           Math2D.ConvertLinePointsToLineSegments(l.OuterRing.Points)));
+                                                           Math2D.ConvertLinePointsToClosingLineSegments(l.OuterRing.Points)));
                 if (!isNear)
                 {
                     return false;
Index: Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsInputValidatorTest.cs
===================================================================
diff -u -r73bd43678d003eca592c2ce14a2500a983d9b4c9 -re678af24e939bdb6b49294b16b06af9565bef9b1
--- Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsInputValidatorTest.cs	(.../MacroStabilityInwardsInputValidatorTest.cs)	(revision 73bd43678d003eca592c2ce14a2500a983d9b4c9)
+++ Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsInputValidatorTest.cs	(.../MacroStabilityInwardsInputValidatorTest.cs)	(revision e678af24e939bdb6b49294b16b06af9565bef9b1)
@@ -602,6 +602,44 @@
                             }))
                         }, new MacroStabilityInwardsPreconsolidationStress[0]))
                 .SetName("X further than x of surfaceLine");
+
+            yield return new TestCaseData(
+                    new MacroStabilityInwardsSoilProfile2D(
+                        "profile",
+                        new[]
+                        {
+                            new MacroStabilityInwardsSoilLayer2D(new Ring(new[]
+                            {
+                                new Point2D(0.2, 0),
+                                new Point2D(0.0, 10),
+                                new Point2D(0.1, 20)
+                            })),
+                            new MacroStabilityInwardsSoilLayer2D(new Ring(new[]
+                            {
+                                new Point2D(0.0, 10.0),
+                                new Point2D(0.1, 20)
+                            }))
+                        }, new MacroStabilityInwardsPreconsolidationStress[0]))
+                .SetName("SoilLayer X start- and endpoint on right side of surfaceline");
+
+            yield return new TestCaseData(
+                    new MacroStabilityInwardsSoilProfile2D(
+                        "profile",
+                        new[]
+                        {
+                            new MacroStabilityInwardsSoilLayer2D(new Ring(new[]
+                            {
+                                new Point2D(0.1, 20),
+                                new Point2D(0.2, 10),
+                                new Point2D(0.0, 10)
+                            })),
+                            new MacroStabilityInwardsSoilLayer2D(new Ring(new[]
+                            {
+                                new Point2D(0.0, 10.0),
+                                new Point2D(0.1, 20)
+                            }))
+                        }, new MacroStabilityInwardsPreconsolidationStress[0]))
+                .SetName("SoilLayer X start- and endpoint on left side of surfaceline");
         }
     }
 }
\ No newline at end of file