Index: DamEngine/trunk/src/Deltares.DamEngine.Calculators/KernelWrappers/MacroStabilityCommon/MacroStabilityCommonHelper.cs
===================================================================
diff -u -r5018 -r5019
--- DamEngine/trunk/src/Deltares.DamEngine.Calculators/KernelWrappers/MacroStabilityCommon/MacroStabilityCommonHelper.cs	(.../MacroStabilityCommonHelper.cs)	(revision 5018)
+++ DamEngine/trunk/src/Deltares.DamEngine.Calculators/KernelWrappers/MacroStabilityCommon/MacroStabilityCommonHelper.cs	(.../MacroStabilityCommonHelper.cs)	(revision 5019)
@@ -417,24 +417,37 @@
     /// <exception cref="ArgumentNullException">Thrown when no SoilProfile2D is defined</exception>
     private static void CombineSoilProfile2DWithSurfaceLine(SoilGeometryProbability subSoilScenario, SurfaceLine2 surfaceLine2, Soil dikeEmbankmentSoil)
     {
+        ValidateForCombineSoilProfile2DWithSurfaceLine(subSoilScenario, surfaceLine2, dikeEmbankmentSoil);
+
+        FitSoilProfile2DToSurfaceLine(subSoilScenario, surfaceLine2);
+    }
+
+    private static void ValidateForCombineSoilProfile2DWithSurfaceLine(SoilGeometryProbability subSoilScenario, SurfaceLine2 surfaceLine2, Soil dikeEmbankmentSoil)
+    {
         if (subSoilScenario.SoilProfile2D == null)
         {
             throw new ArgumentNullException(nameof(subSoilScenario), @"SoilProfile2D cannot be null.");
         }
+
         if (surfaceLine2 == null)
         {
             throw new ArgumentNullException(nameof(surfaceLine2), @"SurfaceLine cannot be null.");
         }
+
         if (dikeEmbankmentSoil == null)
         {
             throw new ArgumentNullException(nameof(dikeEmbankmentSoil), @"DikeEmbankmentSoil cannot be null.");
         }
+
         if (!SoilProfile2DSurfaceLineHelper.IsSurfaceLineAboveBottomSoilProfile2D(surfaceLine2, subSoilScenario.SoilProfile2D))
         {
             throw new InvalidOperationException(@"SurfaceLine is (partly) below the bottom of the SoilProfile2D.");
         }
-        
-        FitSoilProfile2DToSurfaceLine(subSoilScenario, surfaceLine2);
+
+        if (!SurfaceLine2Validator.AreAllCharacteristicPointsXCoordinatesAscending(surfaceLine2))
+        {
+            throw new InvalidOperationException(@"SurfaceLine points are not strictly ascending");
+        }
     }
 
     private static void FitSoilProfile2DToSurfaceLine(SoilGeometryProbability subSoilScenario, SurfaceLine2 surfaceLine2)
Index: DamEngine/trunk/src/Deltares.DamEngine.Data.Tests/Geotechnics/SurfaceLine2ValidatorTests.cs
===================================================================
diff -u
--- DamEngine/trunk/src/Deltares.DamEngine.Data.Tests/Geotechnics/SurfaceLine2ValidatorTests.cs	(revision 0)
+++ DamEngine/trunk/src/Deltares.DamEngine.Data.Tests/Geotechnics/SurfaceLine2ValidatorTests.cs	(revision 5019)
@@ -0,0 +1,37 @@
+// Copyright (C) Stichting Deltares 2024. All rights reserved.
+// 
+// This file is part of the Dam Engine.
+// 
+// The Dam Engine is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+// 
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+// 
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using Deltares.DamEngine.Data.Geotechnics;
+using Deltares.DamEngine.TestHelpers.Factories;
+using NUnit.Framework;
+
+namespace Deltares.DamEngine.Data.Tests.Geotechnics;
+
+[TestFixture]
+public class SurfaceLine2ValidatorTests
+{
+    [Test]
+    public void GivenSurfaceLineWithNonStrictAscendingPointsWhenValidatingThenValidationFails()
+    {
+        SurfaceLine2 surfaceLine = FactoryForSurfaceLines.CreateSurfaceLineDikeNonStrictAscending();
+        Assert.That(SurfaceLine2Validator.AreAllCharacteristicPointsXCoordinatesAscending(surfaceLine), Is.False);
+    }
+}
\ No newline at end of file
Index: DamEngine/trunk/src/Deltares.DamEngine.Data/Geotechnics/SurfaceLine2Validator.cs
===================================================================
diff -u -r5008 -r5019
--- DamEngine/trunk/src/Deltares.DamEngine.Data/Geotechnics/SurfaceLine2Validator.cs	(.../SurfaceLine2Validator.cs)	(revision 5008)
+++ DamEngine/trunk/src/Deltares.DamEngine.Data/Geotechnics/SurfaceLine2Validator.cs	(.../SurfaceLine2Validator.cs)	(revision 5019)
@@ -136,7 +136,7 @@
             {
                 // #Bka: if fact we now should return FALSE immediately but there is a snag. Due to faults with adding characteristic 
                 //       points to a surface line, some surface lines can have identical points (in Location) but with different 
-                //       characteristic (e.g. diktop and trafficload combined). These points should use the same reference to the point
+                //       characteristic (e.g. diketop and trafficload combined). These points should use the same reference to the point
                 //       but it occurs that TWO fysical (and identical) points are added.
                 //       So these points must now be ignored (so identical points must be seen as OK). This is in fact ok for the purpose
                 //       of the validation ast the main problem is that points may never give a vertical part in the geometry.
Index: DamEngine/trunk/src/Deltares.DamEngine.TestHelpers/Factories/FactoryForSurfaceLines.cs
===================================================================
diff -u -r5010 -r5019
--- DamEngine/trunk/src/Deltares.DamEngine.TestHelpers/Factories/FactoryForSurfaceLines.cs	(.../FactoryForSurfaceLines.cs)	(revision 5010)
+++ DamEngine/trunk/src/Deltares.DamEngine.TestHelpers/Factories/FactoryForSurfaceLines.cs	(.../FactoryForSurfaceLines.cs)	(revision 5019)
@@ -831,9 +831,36 @@
     /// <summary>
     /// Creates a surface line, that contains a dike and is cutting the SurfaceLineWithDikeAndDitch. 
     /// </summary>
-    /// <returns>surface line</returns>
+    /// <returns>The surface line</returns>
     public static SurfaceLine2 CreateSurfaceLineCuttingSurfaceLineDikeAndDitch()
     {
         return CreateSurfaceLineDike(-2.0, "AboveSurfaceLineWithDikeAndDitch");
     }
+
+    /// <summary>
+    /// Creates a surface line, that contains a dike and with points that are not strictly ascending.
+    /// </summary>
+    /// <returns>The surface line</returns>
+    public static SurfaceLine2 CreateSurfaceLineDikeNonStrictAscending()
+    {
+        var surfaceLine = new SurfaceLine2
+        {
+            Name = "DikeNonStrictAscending",
+            Geometry = new GeometryPointString(),
+            CharacteristicPoints =
+            {
+                GeometryMustContainPoint = true
+            }
+        };
+
+        surfaceLine.EnsurePointOfType(0.0, 0.0, CharacteristicPointType.SurfaceLevelOutside);
+        surfaceLine.EnsurePointOfType(10.0, 0.0, CharacteristicPointType.DikeToeAtRiver);
+        surfaceLine.EnsurePointOfType(34.5, 5.0, CharacteristicPointType.DikeTopAtRiver);
+        surfaceLine.EnsurePointOfType(40.5, 5.0, CharacteristicPointType.DikeTopAtPolder);
+        surfaceLine.EnsurePointOfType(40.5, 0.0, CharacteristicPointType.DikeToeAtPolder);
+        surfaceLine.EnsurePointOfType(75.0, 0.0, CharacteristicPointType.SurfaceLevelInside);
+
+        surfaceLine.Geometry.SyncCalcPoints();
+        return surfaceLine;
+    }
 }
\ No newline at end of file
Index: DamEngine/trunk/src/Deltares.DamEngine.Calculators.Tests/KernelWrappers/MacroStabilityCommon/MacroStabilityCommonHelperTests.cs
===================================================================
diff -u -r5010 -r5019
--- DamEngine/trunk/src/Deltares.DamEngine.Calculators.Tests/KernelWrappers/MacroStabilityCommon/MacroStabilityCommonHelperTests.cs	(.../MacroStabilityCommonHelperTests.cs)	(revision 5010)
+++ DamEngine/trunk/src/Deltares.DamEngine.Calculators.Tests/KernelWrappers/MacroStabilityCommon/MacroStabilityCommonHelperTests.cs	(.../MacroStabilityCommonHelperTests.cs)	(revision 5019)
@@ -280,6 +280,16 @@
         Assert.Throws<InvalidOperationException>(() => { MacroStabilityCommonHelper.CombineSoilProfileWithSurfaceLine(soilGeometryProbability, surfaceLine, new Soil()); });
     }
 
+    [Test]
+    public void GivenSoilGeometryProbabilityWithSoilProfile2DAndSurfaceLineNonSscanedingWhenCombiningThenExceptionIsRaised()
+    {
+        SoilGeometryProbability soilGeometryProbability = CreateSoilGeometryProbabilityWithSoilProfile2DWithSurfaceLineDitchDike();
+        SurfaceLine2 surfaceLine = FactoryForSurfaceLines.CreateSurfaceLineDikeNonStrictAscending();
+        // Now combine the soilGeometryProbability with the surfaceLine which should in an exception, because the surfaceLine 
+        // is not strictly ascending
+        Assert.Throws<InvalidOperationException>(() => { MacroStabilityCommonHelper.CombineSoilProfileWithSurfaceLine(soilGeometryProbability, surfaceLine, new Soil()); });
+    }
+
     private static SoilGeometryProbability CreateSoilGeometryProbabilityWithSoilProfile2DWithSurfaceLineDitchDike()
     {
         SoilGeometryProbability soilGeometryProbability = FactoryForSoilGeometryProbabilities.CreateSoilGeometryProbabilityWithSoilProfile1D();