Index: Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Service/HeightStructuresCalculationService.cs
===================================================================
diff -u -r636633d6507bef2735fd9b712b3a20feb3ac88c4 -r6279011a954055d718ba3acf1144fc0da8923bf7
--- Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Service/HeightStructuresCalculationService.cs	(.../HeightStructuresCalculationService.cs)	(revision 636633d6507bef2735fd9b712b3a20feb3ac88c4)
+++ Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Service/HeightStructuresCalculationService.cs	(.../HeightStructuresCalculationService.cs)	(revision 6279011a954055d718ba3acf1144fc0da8923bf7)
@@ -221,9 +221,9 @@
             return validationResults.ToArray();
         }
 
-        private static IEnumerable<ValidationRule> GetInputValidationRules(HeightStructuresInput input)
+        private static ValidationRule[] GetInputValidationRules(HeightStructuresInput input)
         {
-            var validationRules = new List<ValidationRule>
+            var validationRules = new ValidationRule[]
             {
                 new UseBreakWaterRule(input),
                 new VariationCoefficientLogNormalDistributionRule(input.StormDuration,