Index: Riskeer/Common/src/Riskeer.Common.Data/Probabilistics/VariationCoefficientDesignVariable.cs
===================================================================
diff -u -rd9119b8f4a74fb2a6f3ececeaea94f0e58513c52 -r085e822eafea9e6e303bbb92972aeb452b5471df
--- Riskeer/Common/src/Riskeer.Common.Data/Probabilistics/VariationCoefficientDesignVariable.cs	(.../VariationCoefficientDesignVariable.cs)	(revision d9119b8f4a74fb2a6f3ececeaea94f0e58513c52)
+++ Riskeer/Common/src/Riskeer.Common.Data/Probabilistics/VariationCoefficientDesignVariable.cs	(.../VariationCoefficientDesignVariable.cs)	(revision 085e822eafea9e6e303bbb92972aeb452b5471df)
@@ -30,7 +30,7 @@
     /// </summary>
     /// <typeparam name="T">The type of the underlying distribution from which a design value is 
     /// derived.</typeparam>
-    public abstract class VariationCoefficientDesignVariable<T> where T : IVariationCoefficientDistribution
+    public abstract class VariationCoefficientDesignVariable<T> where T : class, IVariationCoefficientDistribution
     {
         private T distribution;
 
Index: Riskeer/Common/src/Riskeer.Common.Data/Probabilistics/VariationCoefficientDeterministicDesignVariable.cs
===================================================================
diff -u -rd9119b8f4a74fb2a6f3ececeaea94f0e58513c52 -r085e822eafea9e6e303bbb92972aeb452b5471df
--- Riskeer/Common/src/Riskeer.Common.Data/Probabilistics/VariationCoefficientDeterministicDesignVariable.cs	(.../VariationCoefficientDeterministicDesignVariable.cs)	(revision d9119b8f4a74fb2a6f3ececeaea94f0e58513c52)
+++ Riskeer/Common/src/Riskeer.Common.Data/Probabilistics/VariationCoefficientDeterministicDesignVariable.cs	(.../VariationCoefficientDeterministicDesignVariable.cs)	(revision 085e822eafea9e6e303bbb92972aeb452b5471df)
@@ -29,7 +29,7 @@
     /// </summary>
     /// <typeparam name="T">The type of the variation coefficient distribution.</typeparam>
     public class VariationCoefficientDeterministicDesignVariable<T> : VariationCoefficientDesignVariable<T>
-        where T : IVariationCoefficientDistribution
+        where T : class, IVariationCoefficientDistribution
     {
         private readonly double deterministicValue;
 
Index: Riskeer/Common/src/Riskeer.Common.Forms/PropertyClasses/VariationCoefficientDesignVariableProperties.cs
===================================================================
diff -u -rd9119b8f4a74fb2a6f3ececeaea94f0e58513c52 -r085e822eafea9e6e303bbb92972aeb452b5471df
--- Riskeer/Common/src/Riskeer.Common.Forms/PropertyClasses/VariationCoefficientDesignVariableProperties.cs	(.../VariationCoefficientDesignVariableProperties.cs)	(revision d9119b8f4a74fb2a6f3ececeaea94f0e58513c52)
+++ Riskeer/Common/src/Riskeer.Common.Forms/PropertyClasses/VariationCoefficientDesignVariableProperties.cs	(.../VariationCoefficientDesignVariableProperties.cs)	(revision 085e822eafea9e6e303bbb92972aeb452b5471df)
@@ -34,7 +34,7 @@
     /// <typeparam name="TDistribution">The type of the distribution.</typeparam>
     public abstract class VariationCoefficientDesignVariableProperties<TDistribution>
         : VariationCoefficientDistributionPropertiesBase<TDistribution>
-        where TDistribution : IVariationCoefficientDistribution
+        where TDistribution : class, IVariationCoefficientDistribution
     {
         private readonly VariationCoefficientDesignVariable<TDistribution> designVariable;