Index: Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/LogNormalDistributionRule.cs
===================================================================
diff -u -r6279011a954055d718ba3acf1144fc0da8923bf7 -r023a114d38e9194ffed5f9ee1ee01cc151d80fdb
--- Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/LogNormalDistributionRule.cs	(.../LogNormalDistributionRule.cs)	(revision 6279011a954055d718ba3acf1144fc0da8923bf7)
+++ Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/LogNormalDistributionRule.cs	(.../LogNormalDistributionRule.cs)	(revision 023a114d38e9194ffed5f9ee1ee01cc151d80fdb)
@@ -47,21 +47,17 @@
 
         public override IEnumerable<string> Validate()
         {
-            var validationResults = new List<string>();
-
             if (IsNotConcreteNumber(distribution.Mean))
             {
-                validationResults.Add(string.Format(Resources.ProbabilisticDistributionValidationRule_Mean_of_0_must_be_positive_value,
-                                                    parameterName));
+                yield return string.Format(Resources.ProbabilisticDistributionValidationRule_Mean_of_0_must_be_positive_value,
+                                           parameterName);
             }
 
             if (IsNotConcreteNumber(distribution.StandardDeviation))
             {
-                validationResults.Add(string.Format(Resources.ProbabilisticDistributionValidationRule_StandardDeviation_of_ParameterName_0_must_be_larger_or_equal_to_zero,
-                                                    parameterName));
+                yield return string.Format(Resources.ProbabilisticDistributionValidationRule_StandardDeviation_of_ParameterName_0_must_be_larger_or_equal_to_zero,
+                                           parameterName);
             }
-
-            return validationResults;
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/NormalDistributionRule.cs
===================================================================
diff -u -r6279011a954055d718ba3acf1144fc0da8923bf7 -r023a114d38e9194ffed5f9ee1ee01cc151d80fdb
--- Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/NormalDistributionRule.cs	(.../NormalDistributionRule.cs)	(revision 6279011a954055d718ba3acf1144fc0da8923bf7)
+++ Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/NormalDistributionRule.cs	(.../NormalDistributionRule.cs)	(revision 023a114d38e9194ffed5f9ee1ee01cc151d80fdb)
@@ -47,21 +47,17 @@
 
         public override IEnumerable<string> Validate()
         {
-            var validationResults = new List<string>();
-
             if (IsNotConcreteNumber(distribution.Mean))
             {
-                validationResults.Add(string.Format(Resources.ProbabilisticDistributionValidationRule_Mean_of_0_must_be_a_valid_number,
-                                                    parameterName));
+                yield return string.Format(Resources.ProbabilisticDistributionValidationRule_Mean_of_0_must_be_a_valid_number,
+                                           parameterName);
             }
 
             if (IsNotConcreteNumber(distribution.StandardDeviation))
             {
-                validationResults.Add(string.Format(Resources.ProbabilisticDistributionValidationRule_StandardDeviation_of_ParameterName_0_must_be_larger_or_equal_to_zero,
-                                                    parameterName));
+                yield return string.Format(Resources.ProbabilisticDistributionValidationRule_StandardDeviation_of_ParameterName_0_must_be_larger_or_equal_to_zero,
+                                           parameterName);
             }
-
-            return validationResults;
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/NumericInputRule.cs
===================================================================
diff -u -r6279011a954055d718ba3acf1144fc0da8923bf7 -r023a114d38e9194ffed5f9ee1ee01cc151d80fdb
--- Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/NumericInputRule.cs	(.../NumericInputRule.cs)	(revision 6279011a954055d718ba3acf1144fc0da8923bf7)
+++ Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/NumericInputRule.cs	(.../NumericInputRule.cs)	(revision 023a114d38e9194ffed5f9ee1ee01cc151d80fdb)
@@ -47,15 +47,11 @@
 
         public override IEnumerable<string> Validate()
         {
-            var validationResult = new List<string>();
-
             if (IsNotConcreteNumber(numericInput))
             {
-                validationResult.Add(string.Format(Resources.Validation_ValidateInput_No_concrete_value_entered_for_ParameterName_0_,
-                                                   parameterName));
+                yield return string.Format(Resources.Validation_ValidateInput_No_concrete_value_entered_for_ParameterName_0_,
+                                           parameterName);
             }
-
-            return validationResult;
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/UseBreakWaterRule.cs
===================================================================
diff -u -r6279011a954055d718ba3acf1144fc0da8923bf7 -r023a114d38e9194ffed5f9ee1ee01cc151d80fdb
--- Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/UseBreakWaterRule.cs	(.../UseBreakWaterRule.cs)	(revision 6279011a954055d718ba3acf1144fc0da8923bf7)
+++ Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/UseBreakWaterRule.cs	(.../UseBreakWaterRule.cs)	(revision 023a114d38e9194ffed5f9ee1ee01cc151d80fdb)
@@ -44,14 +44,10 @@
 
         public override IEnumerable<string> Validate()
         {
-            var messages = new List<string>();
-
             if (breakWater.UseBreakWater && IsNotConcreteNumber(breakWater.BreakWater.Height))
             {
-                messages.Add(Resources.Validation_Invalid_BreakWaterHeight_value);
+                yield return Resources.Validation_Invalid_BreakWaterHeight_value;
             }
-
-            return messages;
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/VariationCoefficientLogNormalDistributionRule.cs
===================================================================
diff -u -r6279011a954055d718ba3acf1144fc0da8923bf7 -r023a114d38e9194ffed5f9ee1ee01cc151d80fdb
--- Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/VariationCoefficientLogNormalDistributionRule.cs	(.../VariationCoefficientLogNormalDistributionRule.cs)	(revision 6279011a954055d718ba3acf1144fc0da8923bf7)
+++ Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/VariationCoefficientLogNormalDistributionRule.cs	(.../VariationCoefficientLogNormalDistributionRule.cs)	(revision 023a114d38e9194ffed5f9ee1ee01cc151d80fdb)
@@ -49,21 +49,17 @@
 
         public override IEnumerable<string> Validate()
         {
-            var validationResults = new List<string>();
-
             if (IsNotConcreteNumber(distribution.Mean))
             {
-                validationResults.Add(string.Format(Resources.ProbabilisticDistributionValidationRule_Mean_of_0_must_be_positive_value,
-                                                    parameterName));
+                yield return string.Format(Resources.ProbabilisticDistributionValidationRule_Mean_of_0_must_be_positive_value,
+                                           parameterName);
             }
 
             if (IsNotConcreteNumber(distribution.CoefficientOfVariation))
             {
-                validationResults.Add(string.Format(Resources.ProbabilistiDistributionValidationRule_CoefficientOfVariation_of_ParameterName_0_must_be_larger_or_equal_to_zero,
-                                                    parameterName));
+                yield return string.Format(Resources.ProbabilistiDistributionValidationRule_CoefficientOfVariation_of_ParameterName_0_must_be_larger_or_equal_to_zero,
+                                           parameterName);
             }
-
-            return validationResults;
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/VariationCoefficientNormalDistributionRule.cs
===================================================================
diff -u -r6279011a954055d718ba3acf1144fc0da8923bf7 -r023a114d38e9194ffed5f9ee1ee01cc151d80fdb
--- Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/VariationCoefficientNormalDistributionRule.cs	(.../VariationCoefficientNormalDistributionRule.cs)	(revision 6279011a954055d718ba3acf1144fc0da8923bf7)
+++ Ringtoets/Common/src/Ringtoets.Common.Service/ValidationRules/VariationCoefficientNormalDistributionRule.cs	(.../VariationCoefficientNormalDistributionRule.cs)	(revision 023a114d38e9194ffed5f9ee1ee01cc151d80fdb)
@@ -48,21 +48,17 @@
 
         public override IEnumerable<string> Validate()
         {
-            var validationResults = new List<string>();
-
             if (IsNotConcreteNumber(distribution.Mean))
             {
-                validationResults.Add(string.Format(Resources.ProbabilisticDistributionValidationRule_Mean_of_0_must_be_a_valid_number,
-                                                    parameterName));
+                yield return string.Format(Resources.ProbabilisticDistributionValidationRule_Mean_of_0_must_be_a_valid_number,
+                                           parameterName);
             }
 
             if (IsNotConcreteNumber(distribution.CoefficientOfVariation))
             {
-                validationResults.Add(string.Format(Resources.ProbabilistiDistributionValidationRule_CoefficientOfVariation_of_ParameterName_0_must_be_larger_or_equal_to_zero,
-                                                    parameterName));
+                yield return (string.Format(Resources.ProbabilistiDistributionValidationRule_CoefficientOfVariation_of_ParameterName_0_must_be_larger_or_equal_to_zero,
+                                            parameterName));
             }
-
-            return validationResults;
         }
     }
 }
\ No newline at end of file