Index: Ringtoets/Common/src/Ringtoets.Common.Util/FailureMechanismNormHelper.cs
===================================================================
diff -u -r18fa622cceab5b9575dbf4b6bffd0825100d7416 -r3716307f520488309250ca011e43fe660ecc0e6a
--- Ringtoets/Common/src/Ringtoets.Common.Util/FailureMechanismNormHelper.cs	(.../FailureMechanismNormHelper.cs)	(revision 18fa622cceab5b9575dbf4b6bffd0825100d7416)
+++ Ringtoets/Common/src/Ringtoets.Common.Util/FailureMechanismNormHelper.cs	(.../FailureMechanismNormHelper.cs)	(revision 3716307f520488309250ca011e43fe660ecc0e6a)
@@ -55,7 +55,7 @@
         /// Thrown when:
         /// <list type="bullet">
         /// <item><paramref name="failureMechanismContribution"/> is not in the interval [0.0, 100.0] or is <see cref="double.NaN"/>;</item>
-        /// <item><paramref name="n"/> is not larger than 1 or is <see cref="double.NaN"/>.</item>
+        /// <item><paramref name="n"/> is smaller than 1 or is <see cref="double.NaN"/>.</item>
         /// </list>
         /// </exception>
         public static double GetNorm(IAssessmentSection assessmentSection,
@@ -103,7 +103,7 @@
             if (!Enum.IsDefined(typeof(FailureMechanismCategoryType), categoryType))
             {
                 throw new InvalidEnumArgumentException(nameof(categoryType),
-                                                       (int)categoryType,
+                                                       (int) categoryType,
                                                        typeof(FailureMechanismCategoryType));
             }
 
@@ -120,7 +120,7 @@
 
             if (double.IsNaN(n) || n < 1.0)
             {
-                throw new ArgumentOutOfRangeException(nameof(n), $@"The value for '{nameof(n)}' must be larger than 1.0.");
+                throw new ArgumentOutOfRangeException(nameof(n), $@"The value for '{nameof(n)}' must be 1.0 or larger.");
             }
         }
     }
Index: Ringtoets/Common/test/Ringtoets.Common.Util.Test/FailureMechanismNormHelperTest.cs
===================================================================
diff -u -r18fa622cceab5b9575dbf4b6bffd0825100d7416 -r3716307f520488309250ca011e43fe660ecc0e6a
--- Ringtoets/Common/test/Ringtoets.Common.Util.Test/FailureMechanismNormHelperTest.cs	(.../FailureMechanismNormHelperTest.cs)	(revision 18fa622cceab5b9575dbf4b6bffd0825100d7416)
+++ Ringtoets/Common/test/Ringtoets.Common.Util.Test/FailureMechanismNormHelperTest.cs	(.../FailureMechanismNormHelperTest.cs)	(revision 3716307f520488309250ca011e43fe660ecc0e6a)
@@ -20,7 +20,7 @@
 // All rights reserved.
 
 using System;
-using System.Collections;
+using System.Collections.Generic;
 using System.ComponentModel;
 using Core.Common.TestUtil;
 using NUnit.Framework;
@@ -42,8 +42,8 @@
             // Call
             TestDelegate test = () => FailureMechanismNormHelper.GetNorm(null,
                                                                          FailureMechanismCategoryType.FactorizedLowerLimitNorm,
-                                                                         random.NextDouble(),
-                                                                         random.NextDouble());
+                                                                         random.NextDouble(0, 100),
+                                                                         random.NextDouble(1, 20));
 
             // Assert
             string paramName = Assert.Throws<ArgumentNullException>(test).ParamName;
@@ -60,8 +60,8 @@
             // Call
             TestDelegate test = () => FailureMechanismNormHelper.GetNorm(new AssessmentSectionStub(),
                                                                          (FailureMechanismCategoryType) invalidValue,
-                                                                         random.NextDouble(),
-                                                                         random.NextDouble());
+                                                                         random.NextDouble(0, 100),
+                                                                         random.NextDouble(1, 20));
 
             // Assert
             string expectedMessage = $"The value of argument 'categoryType' ({invalidValue}) is invalid for Enum type '{nameof(FailureMechanismCategoryType)}'.";
@@ -102,11 +102,11 @@
             // Call
             TestDelegate call = () => FailureMechanismNormHelper.GetNorm(new AssessmentSectionStub(),
                                                                          random.NextEnumValue<FailureMechanismCategoryType>(),
-                                                                         random.NextDouble(1, 100),
+                                                                         random.NextDouble(0, 100),
                                                                          n);
 
             // Assert
-            const string message = "The value for 'n' must be larger than 1.0.";
+            const string message = "The value for 'n' must be 1.0 or larger.";
             string paramName = TestHelper.AssertThrowsArgumentExceptionAndTestMessage<ArgumentOutOfRangeException>(call, message).ParamName;
             Assert.AreEqual("n", paramName);
         }
@@ -127,7 +127,7 @@
             Assert.AreEqual(expectedNorm, norm, 1e-5);
         }
 
-        private static IEnumerable GetNormConfigurationPerFailureMechanismCategoryType()
+        private static IEnumerable<TestCaseData> GetNormConfigurationPerFailureMechanismCategoryType()
         {
             const double signalingNorm = 0.002;
             const double lowerLimitNorm = 0.005;
Index: Ringtoets/GrassCoverErosionOutwards/src/Ringtoets.GrassCoverErosionOutwards.Data/GrassCoverErosionOutwardsFailureMechanismExtensions.cs
===================================================================
diff -u -r9e2f7186181853ea7cce697f737eeca21f82551f -r3716307f520488309250ca011e43fe660ecc0e6a
--- Ringtoets/GrassCoverErosionOutwards/src/Ringtoets.GrassCoverErosionOutwards.Data/GrassCoverErosionOutwardsFailureMechanismExtensions.cs	(.../GrassCoverErosionOutwardsFailureMechanismExtensions.cs)	(revision 9e2f7186181853ea7cce697f737eeca21f82551f)
+++ Ringtoets/GrassCoverErosionOutwards/src/Ringtoets.GrassCoverErosionOutwards.Data/GrassCoverErosionOutwardsFailureMechanismExtensions.cs	(.../GrassCoverErosionOutwardsFailureMechanismExtensions.cs)	(revision 3716307f520488309250ca011e43fe660ecc0e6a)
@@ -127,13 +127,6 @@
                 throw new ArgumentNullException(nameof(failureMechanism));
             }
 
-            if (!Enum.IsDefined(typeof(FailureMechanismCategoryType), categoryType))
-            {
-                throw new InvalidEnumArgumentException(nameof(categoryType),
-                                                       (int) categoryType,
-                                                       typeof(FailureMechanismCategoryType));
-            }
-
             return FailureMechanismNormHelper.GetNorm(assessmentSection,
                                                       categoryType,
                                                       failureMechanism.Contribution,