Index: Ringtoets/Storage/src/Ringtoets.Storage.Core/Serializers/TangentLinesXmlSerializer.cs
===================================================================
diff -u -r92a7d5fbc462aa16be6eba11ba9e7b54fcd38622 -r8bb0a6cc01c87aaeac272c6d2c5eaaa0d9e265ab
--- Ringtoets/Storage/src/Ringtoets.Storage.Core/Serializers/TangentLinesXmlSerializer.cs	(.../TangentLinesXmlSerializer.cs)	(revision 92a7d5fbc462aa16be6eba11ba9e7b54fcd38622)
+++ Ringtoets/Storage/src/Ringtoets.Storage.Core/Serializers/TangentLinesXmlSerializer.cs	(.../TangentLinesXmlSerializer.cs)	(revision 8bb0a6cc01c87aaeac272c6d2c5eaaa0d9e265ab)
@@ -22,6 +22,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.Serialization;
 using Core.Common.Base.Data;
 
 namespace Ringtoets.Storage.Core.Serializers
@@ -42,8 +43,10 @@
         }
 
         [Serializable]
+        [DataContract(Name = nameof(SerializableTangentLine), Namespace = "")]
         internal class SerializableTangentLine
         {
+            [DataMember]
             private readonly double tangentLine;
 
             /// <summary>
Index: Ringtoets/Storage/test/Ringtoets.Storage.Core.Test/Serializers/TangentLinesXmlSerializerTest.cs
===================================================================
diff -u -r228865ccc3e9aa485f6497ef7b2bb70766120122 -r8bb0a6cc01c87aaeac272c6d2c5eaaa0d9e265ab
--- Ringtoets/Storage/test/Ringtoets.Storage.Core.Test/Serializers/TangentLinesXmlSerializerTest.cs	(.../TangentLinesXmlSerializerTest.cs)	(revision 228865ccc3e9aa485f6497ef7b2bb70766120122)
+++ Ringtoets/Storage/test/Ringtoets.Storage.Core.Test/Serializers/TangentLinesXmlSerializerTest.cs	(.../TangentLinesXmlSerializerTest.cs)	(revision 8bb0a6cc01c87aaeac272c6d2c5eaaa0d9e265ab)
@@ -24,6 +24,7 @@
 using Core.Common.TestUtil;
 using NUnit.Framework;
 using Ringtoets.Storage.Core.Serializers;
+using Ringtoets.Storage.Core.TestUtil.Serializers;
 
 namespace Ringtoets.Storage.Core.Test.Serializers
 {
@@ -38,6 +39,7 @@
 
             // Assert
             Assert.IsInstanceOf<DataCollectionSerializer<RoundedDouble, TangentLinesXmlSerializer.SerializableTangentLine>>(serializer);
+            SerializerTestHelper.AssertSerializedData<TangentLinesXmlSerializer.SerializableTangentLine>();
         }
 
         [Test]