Index: Ringtoets/MacroStabilityInwards/src/Ringtoets.MacroStabilityInwards.Service/MacroStabilityInwardsInputValidator.cs
===================================================================
diff -u -ra5907a9c3b963642ff426af2ed7e4a9a146c2556 -rb231bcbf451d747c2ed6f828f320cececad73ece
--- Ringtoets/MacroStabilityInwards/src/Ringtoets.MacroStabilityInwards.Service/MacroStabilityInwardsInputValidator.cs	(.../MacroStabilityInwardsInputValidator.cs)	(revision a5907a9c3b963642ff426af2ed7e4a9a146c2556)
+++ Ringtoets/MacroStabilityInwards/src/Ringtoets.MacroStabilityInwards.Service/MacroStabilityInwardsInputValidator.cs	(.../MacroStabilityInwardsInputValidator.cs)	(revision b231bcbf451d747c2ed6f828f320cececad73ece)
@@ -175,20 +175,58 @@
             double maximumXCoordinateSoilProfile = soilProfileXCoordinates.Max();
             double maxXCoordinate = Math.Min(maximumXCoordinateSoilProfile, maximumXCoordinateSurfaceLine);
 
-            var xCoordinates = new List<double>();
             double minimumXCoordinateSurfaceLine = surfaceLineXCoordinates.Min();
             double minimumXCoordinateSoilProfile = soilProfileXCoordinates.Min();
-            double x = Math.Max(minimumXCoordinateSoilProfile, minimumXCoordinateSurfaceLine);
-            while (x < maxXCoordinate)
+            double minXCoordinate = Math.Max(minimumXCoordinateSoilProfile, minimumXCoordinateSurfaceLine);
+
+            IEnumerable<double> clippedSoilProfileXCoordinates = soilProfileXCoordinates.Where(xCoordinate => IsXCoordinateInRange(xCoordinate, minXCoordinate, maxXCoordinate));
+            IEnumerable<double> clippedSurfaceLineXCoordinates = surfaceLineXCoordinates.Where(xCoordinate => IsXCoordinateInRange(xCoordinate, minXCoordinate, maxXCoordinate));
+
+            double[] uniqueClippedXCoordinates = clippedSoilProfileXCoordinates.Concat(clippedSurfaceLineXCoordinates)
+                                                                               .Distinct()
+                                                                               .OrderBy(xCoordinate => xCoordinate)
+                                                                               .ToArray();
+
+            var xCoordinates = new List<double>();
+            for (var i = 0; i < uniqueClippedXCoordinates.Length - 1; i++)
             {
-                xCoordinates.Add(x);
-                x += withinSurfaceLineLevelLimit;
+                double firstXCoordinate = uniqueClippedXCoordinates[i];
+                double secondXCoordinate = uniqueClippedXCoordinates[i + 1];
+
+                xCoordinates.AddRange(GetDiscretizedXCoordinatesBetweenInterval(firstXCoordinate, secondXCoordinate));
             }
-            xCoordinates.Add(maxXCoordinate);
+            xCoordinates.Add(uniqueClippedXCoordinates.Last());
 
             return xCoordinates;
         }
 
+        private static IEnumerable<double> GetDiscretizedXCoordinatesBetweenInterval(double startXCoordinate, double endXCoordinate)
+        {
+            if (Math.Abs(endXCoordinate - startXCoordinate) < withinSurfaceLineLevelLimit)
+            {
+                return new[]
+                {
+                    startXCoordinate
+                };
+            }
+
+            double xCoordinate = startXCoordinate;
+            var discretizedXCoordinates = new List<double>();
+            while (xCoordinate < endXCoordinate)
+            {
+                discretizedXCoordinates.Add(xCoordinate);
+                xCoordinate += withinSurfaceLineLevelLimit;
+            }
+
+            return discretizedXCoordinates;
+        }
+
+        private static bool IsXCoordinateInRange(double xCoordinate, double minXCoordinate, double maxXCoordinate)
+        {
+            return xCoordinate <= maxXCoordinate
+                   && xCoordinate >= minXCoordinate;
+        }
+
         private static IEnumerable<IEnumerable<Segment2D>> GetLayerPolygons(MacroStabilityInwardsSoilProfile2D soilProfile2D)
         {
             return soilProfile2D.Layers
Index: Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsInputValidatorTest.cs
===================================================================
diff -u -rba06f85a75504d30e937dcbce92f08ea31ca9e49 -rb231bcbf451d747c2ed6f828f320cececad73ece
--- Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsInputValidatorTest.cs	(.../MacroStabilityInwardsInputValidatorTest.cs)	(revision ba06f85a75504d30e937dcbce92f08ea31ca9e49)
+++ Ringtoets/MacroStabilityInwards/test/Ringtoets.MacroStabilityInwards.Service.Test/MacroStabilityInwardsInputValidatorTest.cs	(.../MacroStabilityInwardsInputValidatorTest.cs)	(revision b231bcbf451d747c2ed6f828f320cececad73ece)
@@ -399,6 +399,64 @@
         }
 
         /// <remarks>
+        /// The soil profile used in this test contains one outer layer (outer ring) and a surfaceline:
+        /// <item>Soil layer (X) is defined as shown below:</item>
+        /// <code>
+        ///                                           
+        ///   20   X              X ---------------- X
+        ///        | \           /                   |
+        ///        |  \         /                    |
+        ///   15   |   \       /                     |
+        ///        |    \     /                      |
+        ///        |     \   /                       |
+        ///   10   |       X                         |
+        ///        |                                 |
+        ///        |                                 |
+        ///    5   X ------------------------------- X
+        ///        0     0.025   0.05      ...      0.2
+        /// </code>
+        /// </remarks>
+        [Test]
+        public void Validate_SurfaceLineNear2DProfileWithLayersWithSmallInflectionDefinition_ReturnsError()
+        {
+            // Setup
+            var surfaceLine = new MacroStabilityInwardsSurfaceLine("Test");
+            surfaceLine.SetGeometry(new[]
+            {
+                new Point3D(0, 0.0, 20),
+                new Point3D(0.2, 0.0, 20)
+            });
+
+            var soilProfile = new MacroStabilityInwardsSoilProfile2D(
+                "profile",
+                new[]
+                {
+                    new MacroStabilityInwardsSoilLayer2D(new Ring(new[]
+                    {
+                        new Point2D(0, 20),
+                        new Point2D(0.025, 10),
+                        new Point2D(0.05, 20),
+                        new Point2D(0.2, 20),
+                        new Point2D(0.2, 5), 
+                        new Point2D(0, 5) 
+                    }))
+                }, new MacroStabilityInwardsPreconsolidationStress[0]);
+
+            input.StochasticSoilProfile = new MacroStabilityInwardsStochasticSoilProfile(0.0,
+                                                                                         soilProfile);
+            input.SurfaceLine = surfaceLine;
+
+            // Call
+            IEnumerable<string> messages = MacroStabilityInwardsInputValidator.Validate(input).ToArray();
+
+            // Assert
+            CollectionAssert.AreEqual(new[]
+            {
+                "De profielschematisatie moet op de ondergrondschematisatie liggen."
+            }, messages);
+        }
+
+        /// <remarks>
         /// The soil profile used in this test contains two outer layers (outer rings) and a surfaceline:
         /// <list type="bullet">
         /// <item>Soil layer (1) is defined as shown below:
@@ -869,7 +927,7 @@
                                                       new Point2D(0, 10),
                                                       new Point2D(1, 20),
                                                       new Point2D(2, 10)
-                                                  })),
+                                                  }))
                                               }, new MacroStabilityInwardsPreconsolidationStress[0]))
                 .SetName("Top soilLayer offset above surfaceline and not within limit");
         }