Index: Ringtoets/Integration/src/Ringtoets.Integration.IO/Creators/SerializableAssemblyCreator.cs
===================================================================
diff -u -r0526b2313fd2c2bf90766d83f2a815037d01b9c9 -r0df4def16c2d4e4cb3be9a65fc94422a602d330c
--- Ringtoets/Integration/src/Ringtoets.Integration.IO/Creators/SerializableAssemblyCreator.cs	(.../SerializableAssemblyCreator.cs)	(revision 0526b2313fd2c2bf90766d83f2a815037d01b9c9)
+++ Ringtoets/Integration/src/Ringtoets.Integration.IO/Creators/SerializableAssemblyCreator.cs	(.../SerializableAssemblyCreator.cs)	(revision 0df4def16c2d4e4cb3be9a65fc94422a602d330c)
@@ -51,7 +51,7 @@
             }
 
             var idGenerator = new UniqueIdentifierGenerator();
-            string serializableAssemblyId = idGenerator.GetNewId().ToString();
+            string serializableAssemblyId = idGenerator.GetNewId();
 
             return new SerializableAssembly(serializableAssemblyId,
                                             GetLowerCorner(assessmentSection.Geometry),
Index: Ringtoets/Integration/src/Ringtoets.Integration.IO/Creators/SerializableAssessmentSectionCreator.cs
===================================================================
diff -u -r0526b2313fd2c2bf90766d83f2a815037d01b9c9 -r0df4def16c2d4e4cb3be9a65fc94422a602d330c
--- Ringtoets/Integration/src/Ringtoets.Integration.IO/Creators/SerializableAssessmentSectionCreator.cs	(.../SerializableAssessmentSectionCreator.cs)	(revision 0526b2313fd2c2bf90766d83f2a815037d01b9c9)
+++ Ringtoets/Integration/src/Ringtoets.Integration.IO/Creators/SerializableAssessmentSectionCreator.cs	(.../SerializableAssessmentSectionCreator.cs)	(revision 0df4def16c2d4e4cb3be9a65fc94422a602d330c)
@@ -51,7 +51,7 @@
                 throw new ArgumentNullException(nameof(idGenerator));
             }
 
-            return new SerializableAssessmentSection(idGenerator.GetNewId().ToString(),
+            return new SerializableAssessmentSection(idGenerator.GetNewId(),
                                                      assessmentSectionName,
                                                      geometry);
         }
Index: Ringtoets/Integration/src/Ringtoets.Integration.IO/Helpers/UniqueIdentifierGenerator.cs
===================================================================
diff -u -r77af63e3ae290bffd192ac96059661e15181c775 -r0df4def16c2d4e4cb3be9a65fc94422a602d330c
--- Ringtoets/Integration/src/Ringtoets.Integration.IO/Helpers/UniqueIdentifierGenerator.cs	(.../UniqueIdentifierGenerator.cs)	(revision 77af63e3ae290bffd192ac96059661e15181c775)
+++ Ringtoets/Integration/src/Ringtoets.Integration.IO/Helpers/UniqueIdentifierGenerator.cs	(.../UniqueIdentifierGenerator.cs)	(revision 0df4def16c2d4e4cb3be9a65fc94422a602d330c)
@@ -40,9 +40,9 @@
         /// Gets a new unique id.
         /// </summary>
         /// <returns>An unique id.</returns>
-        public int GetNewId()
+        public string GetNewId()
         {
-            return currentId++;
+            return $"{currentId++}";
         }
     }
 }
\ No newline at end of file
Index: Ringtoets/Integration/test/Ringtoets.Integration.IO.Test/Helpers/UniqueIdentifierGeneratorTest.cs
===================================================================
diff -u -r77af63e3ae290bffd192ac96059661e15181c775 -r0df4def16c2d4e4cb3be9a65fc94422a602d330c
--- Ringtoets/Integration/test/Ringtoets.Integration.IO.Test/Helpers/UniqueIdentifierGeneratorTest.cs	(.../UniqueIdentifierGeneratorTest.cs)	(revision 77af63e3ae290bffd192ac96059661e15181c775)
+++ Ringtoets/Integration/test/Ringtoets.Integration.IO.Test/Helpers/UniqueIdentifierGeneratorTest.cs	(.../UniqueIdentifierGeneratorTest.cs)	(revision 0df4def16c2d4e4cb3be9a65fc94422a602d330c)
@@ -19,7 +19,6 @@
 // Stichting Deltares and remain full property of Stichting Deltares at all times.
 // All rights reserved.
 
-using System.Collections.Generic;
 using NUnit.Framework;
 using Ringtoets.Integration.IO.Helpers;
 
@@ -35,24 +34,24 @@
             var generator = new UniqueIdentifierGenerator();
 
             // Call
-            int id = generator.GetNewId();
+            string id = generator.GetNewId();
 
             // Assert
-            Assert.Zero(id);
+            Assert.AreEqual("0", id);
         }
 
         [Test]
         public void GivenGeneratedId_WhenGetNewIdCalled_ThenNewIdGenerated()
         {
             // Given
             var generator = new UniqueIdentifierGenerator();
-            int currentId = generator.GetNewId();
+            string currentId = generator.GetNewId();
 
             // Precondition
-            Assert.Zero(currentId);
+            Assert.AreEqual("0", currentId);
 
             // When
-            var generatedIds = new List<int>
+            string[] generatedIds =
             {
                 generator.GetNewId(),
                 generator.GetNewId()
@@ -61,8 +60,8 @@
             // Then
             CollectionAssert.AreEqual(new[]
             {
-                1,
-                2
+                "1",
+                "2"
             }, generatedIds);
         }
     }