Index: DamEngine/trunk/src/Deltares.DamEngine.Data.Tests/Geotechnics/GeometryHelperTests.cs
===================================================================
diff -u -r4866 -r4873
--- DamEngine/trunk/src/Deltares.DamEngine.Data.Tests/Geotechnics/GeometryHelperTests.cs	(.../GeometryHelperTests.cs)	(revision 4866)
+++ DamEngine/trunk/src/Deltares.DamEngine.Data.Tests/Geotechnics/GeometryHelperTests.cs	(.../GeometryHelperTests.cs)	(revision 4873)
@@ -19,6 +19,7 @@
 // Stichting Deltares and remain full property of Stichting Deltares at all times.
 // All rights reserved.
 
+using System;
 using Deltares.DamEngine.Data.Geometry;
 using Deltares.DamEngine.Data.Geotechnics;
 using Deltares.DamEngine.TestHelpers.Factories;
@@ -29,6 +30,12 @@
 [TestFixture]
 public class GeometryHelperTests
 {
+    // For debugging purposes
+    private const string visualizationFolder = @"D:\src\dam\DamTools\GeometryVisualizer\";
+    // Use the following code to export the geometry to a file
+    // GeometryExporter.ExportToFile(soilProfile2D.Geometry, visualizationFolder + "Geometry.txt");
+    // GeometryExporter.ExportToJsonFile(soilProfile2D.Geometry, visualizationFolder + "Geometry.json");
+
     const double cTolerance = 1e-6;
 
     [Test]
@@ -45,15 +52,35 @@
     }
 
     [Test]
-    public void GivenTwoLayerGeometryWhenExtendingRigthThenLeftBoundaryIsChanged()
+    public void GivenTwoLayerGeometryWhenExtendingLeftToTheRightThenExceptionIsThrown()
     {
         // Given
         SoilProfile2D soilProfile2D = FactoryForSoilProfiles.CreateSoilProfile2DWithTwoLayers();
 
+        // When & Then
+        Assert.Throws<ArgumentException>(() => { GeometryHelper.ExtendGeometryLeft(soilProfile2D.Geometry, 2); });
+    }
+
+    [Test]
+    public void GivenTwoLayerGeometryWhenExtendingRightThenLeftBoundaryIsChanged()
+    {
+        // Given
+        SoilProfile2D soilProfile2D = FactoryForSoilProfiles.CreateSoilProfile2DWithTwoLayers();
+
         // When
-        GeometryHelper.ExtendGeometryRight(soilProfile2D.Geometry, 12);
+        GeometryHelper.ExtendGeometryRight(soilProfile2D.Geometry, 8);
 
         // Then
         Assert.That(soilProfile2D.Geometry.Right, Is.EqualTo(12).Within(cTolerance));
     }
+
+    [Test]
+    public void GivenTwoLayerGeometryWhenExtendingRightToTheLeftThenExpceptionIsThrown()
+    {
+        // Given
+        SoilProfile2D soilProfile2D = FactoryForSoilProfiles.CreateSoilProfile2DWithTwoLayers();
+
+        // When & Then
+        Assert.Throws<ArgumentException>(() => { GeometryHelper.ExtendGeometryRight(soilProfile2D.Geometry, 8); });
+    }
 }
\ No newline at end of file
Index: DamEngine/trunk/src/Deltares.DamEngine.Data/Geometry/GeometryHelper.cs
===================================================================
diff -u -r4866 -r4873
--- DamEngine/trunk/src/Deltares.DamEngine.Data/Geometry/GeometryHelper.cs	(.../GeometryHelper.cs)	(revision 4866)
+++ DamEngine/trunk/src/Deltares.DamEngine.Data/Geometry/GeometryHelper.cs	(.../GeometryHelper.cs)	(revision 4873)
@@ -34,6 +34,11 @@
     /// <param name="toX">The x position to move the boundary to.</param>
     public static void ExtendGeometryLeft(GeometryData geometry, double toX)
     {
+        if (toX > geometry.Left)
+        {
+            throw new ArgumentException("The new left boundary should be smaller than the current left boundary.");
+        }
+
         Point2D[] leftPoints = geometry.GetLeftPoints().OrderBy(x => x.Z).ToArray();
         List<GeometryCurve> leftCurves = geometry.GetLeftCurves();
         Point2D prevPoint = null;
@@ -72,6 +77,11 @@
     /// <param name="toX">The x position to move the boundary to.</param>
     public static void ExtendGeometryRight(GeometryData geometry, double toX)
     {
+        if (toX < geometry.Right)
+        {
+            throw new ArgumentException("The new right boundary should be larger than the current right boundary.");
+        }
+
         Point2D[] rightPoints = geometry.GetRightPoints().OrderBy(x => x.Z).ToArray();
         List<GeometryCurve> rightCurves = geometry.GetRightCurves();
         Point2D prevPoint = null;