Index: Ringtoets/AssemblyTool/src/Ringtoets.AssemblyTool.KernelWrapper/Calculators/Assembly/FailureMechanismSectionAssemblyCalculator.cs
===================================================================
diff -u -r66d6f7a3b583d9bca7b5a9c9697f8f4f332cc5c9 -re435a360ae5009cfba77b9ca859c8880945d5781
--- Ringtoets/AssemblyTool/src/Ringtoets.AssemblyTool.KernelWrapper/Calculators/Assembly/FailureMechanismSectionAssemblyCalculator.cs	(.../FailureMechanismSectionAssemblyCalculator.cs)	(revision 66d6f7a3b583d9bca7b5a9c9697f8f4f332cc5c9)
+++ Ringtoets/AssemblyTool/src/Ringtoets.AssemblyTool.KernelWrapper/Calculators/Assembly/FailureMechanismSectionAssemblyCalculator.cs	(.../FailureMechanismSectionAssemblyCalculator.cs)	(revision e435a360ae5009cfba77b9ca859c8880945d5781)
@@ -305,7 +305,7 @@
             {
                 FmSectionAssemblyDirectResult simpleAssemblyResult = 
                     FailureMechanismSectionAssemblyCalculatorInputCreator.CreateFailureMechanismSectionAssemblyDirectResult(simpleAssembly);
-                if (simpleAssemblyResult.Result == EFmSectionCategory.NotApplicable)
+                if (simpleAssemblyResult.Result == EFmSectionCategory.NotApplicable || simpleAssemblyResult.Result == EFmSectionCategory.Iv)
                 {
                     return FailureMechanismSectionAssemblyCreator.Create(simpleAssemblyResult);
                 }
@@ -332,14 +332,14 @@
             {
                 FmSectionAssemblyDirectResult simpleAssemblyResult = 
                     FailureMechanismSectionAssemblyCalculatorInputCreator.CreateFailureMechanismSectionAssemblyDirectResult(simpleAssembly);
-                if (simpleAssemblyResult.Result == EFmSectionCategory.NotApplicable)
+                if (simpleAssemblyResult.Result == EFmSectionCategory.NotApplicable || simpleAssemblyResult.Result == EFmSectionCategory.Iv)
                 {
                     return FailureMechanismSectionAssemblyCreator.CreateFailureMechanismSectionAssemblyCategoryGroup(simpleAssemblyResult.Result);
                 }
 
                 IFailureMechanismSectionAssemblyCalculatorKernel kernel = factory.CreateFailureMechanismSectionAssemblyKernel();
                 var output = (FmSectionAssemblyDirectResult) kernel.TranslateAssessmentResultWbi0A1(
-                    FailureMechanismSectionAssemblyCalculatorInputCreator.CreateFailureMechanismSectionAssemblyDirectResult(simpleAssembly),
+                    simpleAssemblyResult,
                     FailureMechanismSectionAssemblyCalculatorInputCreator.CreateFailureMechanismSectionAssemblyDirectResult(detailedAssembly),
                     FailureMechanismSectionAssemblyCalculatorInputCreator.CreateFailureMechanismSectionAssemblyDirectResult(tailorMadeAssembly));
 
Index: Ringtoets/AssemblyTool/test/Ringtoets.AssemblyTool.KernelWrapper.Test/Calculators/Assembly/FailureMechanismSectionAssemblyCalculatorTest.cs
===================================================================
diff -u -r3d4e5f465e7effc3d1691bb5920ff06806d26d32 -re435a360ae5009cfba77b9ca859c8880945d5781
--- Ringtoets/AssemblyTool/test/Ringtoets.AssemblyTool.KernelWrapper.Test/Calculators/Assembly/FailureMechanismSectionAssemblyCalculatorTest.cs	(.../FailureMechanismSectionAssemblyCalculatorTest.cs)	(revision 3d4e5f465e7effc3d1691bb5920ff06806d26d32)
+++ Ringtoets/AssemblyTool/test/Ringtoets.AssemblyTool.KernelWrapper.Test/Calculators/Assembly/FailureMechanismSectionAssemblyCalculatorTest.cs	(.../FailureMechanismSectionAssemblyCalculatorTest.cs)	(revision e435a360ae5009cfba77b9ca859c8880945d5781)
@@ -1755,7 +1755,7 @@
         {
             // Setup
             var random = new Random(39);
-            var simpleAssembly = new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>());
+            var simpleAssembly = new FailureMechanismSectionAssembly(random.NextDouble(), FailureMechanismSectionAssemblyCategoryGroup.None);
             var detailedAssembly = new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>());
             var tailorMadeAssembly = new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>());
 
@@ -1779,11 +1779,14 @@
         }
 
         [Test]
-        public void AssembleCombinedWithProbabilities_WithSimpleAssemblyNotApplicable_ExpectedOutputReturnedByCalculator()
+        [TestCase(FailureMechanismSectionAssemblyCategoryGroup.NotApplicable)]
+        [TestCase(FailureMechanismSectionAssemblyCategoryGroup.Iv)]
+        public void AssembleCombinedWithProbabilities_WithSimpleAssemblyNotApplicableOrCategoryIv_ExpectedOutputReturnedByCalculator(
+            FailureMechanismSectionAssemblyCategoryGroup category)
         {
             // Setup
             var random = new Random(39);
-            var simpleAssembly = new FailureMechanismSectionAssembly(random.NextDouble(), FailureMechanismSectionAssemblyCategoryGroup.NotApplicable);
+            var simpleAssembly = new FailureMechanismSectionAssembly(random.NextDouble(), category);
             var detailedAssembly = new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>());
             var tailorMadeAssembly = new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>());
 
@@ -1848,8 +1851,8 @@
 
                 // Call
                 TestDelegate test = () => calculator.AssembleCombined(
+                    new FailureMechanismSectionAssembly(random.NextDouble(), FailureMechanismSectionAssemblyCategoryGroup.None),
                     new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>()),
-                    new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>()),
                     new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>()));
 
                 // Assert
@@ -1876,8 +1879,8 @@
 
                 // Call
                 TestDelegate test = () => calculator.AssembleCombined(
+                    new FailureMechanismSectionAssembly(random.NextDouble(), FailureMechanismSectionAssemblyCategoryGroup.None),
                     new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>()),
-                    new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>()),
                     new FailureMechanismSectionAssembly(random.NextDouble(), random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>()));
 
                 // Assert
@@ -1917,7 +1920,7 @@
         {
             // Setup
             var random = new Random(39);
-            var simpleAssembly = random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>();
+            var simpleAssembly = FailureMechanismSectionAssemblyCategoryGroup.None;
             var detailedAssembly = random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>();
             var tailorMadeAssembly = random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>();
 
@@ -1940,11 +1943,14 @@
         }
 
         [Test]
-        public void AssembleCombined_WithSimpleAssemblyNotApplicable_ExpectedOutputReturnedByCalculator()
+        [TestCase(FailureMechanismSectionAssemblyCategoryGroup.NotApplicable)]
+        [TestCase(FailureMechanismSectionAssemblyCategoryGroup.Iv)]
+        public void AssembleCombined_WithSimpleAssemblyNotApplicableOrCategoryIv_ExpectedOutputReturnedByCalculator(
+            FailureMechanismSectionAssemblyCategoryGroup category)
         {
             // Setup
             var random = new Random(39);
-            const FailureMechanismSectionAssemblyCategoryGroup simpleAssembly = FailureMechanismSectionAssemblyCategoryGroup.NotApplicable;
+            FailureMechanismSectionAssemblyCategoryGroup simpleAssembly = category;
             var detailedAssembly = random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>();
             var tailorMadeAssembly = random.NextEnumValue<FailureMechanismSectionAssemblyCategoryGroup>();
 
@@ -1960,7 +1966,7 @@
                 FailureMechanismSectionAssemblyCategoryGroup assembly = calculator.AssembleCombined(simpleAssembly, detailedAssembly, tailorMadeAssembly);
 
                 // Assert
-                Assert.AreEqual(FailureMechanismSectionAssemblyCategoryGroup.NotApplicable, assembly);
+                Assert.AreEqual(simpleAssembly, assembly);
             }
         }