Index: Ringtoets/Migration/src/Ringtoets.Migration.Core/EmbeddedResources/Migration_17.3_18.1.sql
===================================================================
diff -u -rce6ccec78e3c63aafd8f24b5ad64a7d3660f9312 -r1e4c6b136ad2a302091e0c121d2644054a594a87
--- Ringtoets/Migration/src/Ringtoets.Migration.Core/EmbeddedResources/Migration_17.3_18.1.sql	(.../Migration_17.3_18.1.sql)	(revision ce6ccec78e3c63aafd8f24b5ad64a7d3660f9312)
+++ Ringtoets/Migration/src/Ringtoets.Migration.Core/EmbeddedResources/Migration_17.3_18.1.sql	(.../Migration_17.3_18.1.sql)	(revision 1e4c6b136ad2a302091e0c121d2644054a594a87)
@@ -76,7 +76,12 @@
 			[ProbabilityOrFrequencyOpenStructureBeforeFlooding]
 	END,
 	[FailureProbabilityOpenStructure],
-	[IdenticalApertures],
+	CASE
+		WHEN [IdenticalApertures] = 0
+			THEN 1
+		ELSE 
+			[IdenticalApertures]
+	END,
 	[FailureProbabilityReparation],
 	[InflowModelType]
 FROM [SOURCEPROJECT].ClosingStructureEntity;
Index: Ringtoets/Migration/test/Ringtoets.Migration.Core.Test/test-data/MigrationTestProject173.rtd
===================================================================
diff -u -r0bf23391f0e54ec81094b93b84ae9b3ac511ecff -r1e4c6b136ad2a302091e0c121d2644054a594a87
Binary files differ
Index: Ringtoets/Migration/test/Ringtoets.Migration.Integration.Test/MigrationTo181IntegrationTest.cs
===================================================================
diff -u -rce6ccec78e3c63aafd8f24b5ad64a7d3660f9312 -r1e4c6b136ad2a302091e0c121d2644054a594a87
--- Ringtoets/Migration/test/Ringtoets.Migration.Integration.Test/MigrationTo181IntegrationTest.cs	(.../MigrationTo181IntegrationTest.cs)	(revision ce6ccec78e3c63aafd8f24b5ad64a7d3660f9312)
+++ Ringtoets/Migration/test/Ringtoets.Migration.Integration.Test/MigrationTo181IntegrationTest.cs	(.../MigrationTo181IntegrationTest.cs)	(revision 1e4c6b136ad2a302091e0c121d2644054a594a87)
@@ -158,6 +158,25 @@
                 "DETACH DATABASE SOURCEPROJECT;";
             reader.AssertReturnedDataIsValid(validateClosingStructureProbabilityOpenStructureBeforeFlooding);
 
+            string validateIdenticalApertures =
+                $"ATTACH DATABASE \"{sourceFilePath}\" AS SOURCEPROJECT; " +
+                "SELECT " +
+                "SUM([IsInvalid]) = 0 " +
+                "FROM " +
+                "( " +
+                "SELECT " +
+                "CASE WHEN (NEW.[IdenticalApertures] != OLD.[IdenticalApertures] " +
+                "AND OLD.[IdenticalApertures] >= 1)  " +
+                "OR (NEW.[IdenticalApertures] != 1 AND OLD.[IdenticalApertures] = 0) " +
+                "THEN 1 " +
+                "ELSE 0 " +
+                "END AS [IsInvalid] " +
+                "FROM ClosingStructureEntity NEW " +
+                "JOIN [SOURCEPROJECT].ClosingStructureEntity OLD USING (ClosingStructureEntityId) " +
+                "); " +
+                "DETACH DATABASE SOURCEPROJECT;";
+            reader.AssertReturnedDataIsValid(validateIdenticalApertures);
+
             string validateClosingStructure =
                 $"ATTACH DATABASE \"{sourceFilePath}\" AS SOURCEPROJECT; " +
                 "SELECT COUNT() = (SELECT COUNT() FROM [SOURCEPROJECT].ClosingStructureEntity) " +
@@ -188,7 +207,6 @@
                 "AND NEW.FlowWidthAtBottomProtectionMean IS OLD.FlowWidthAtBottomProtectionMean" +
                 "AND NEW.FlowWidthAtBottomProtectionStandardDeviation IS OLD.FlowWidthAtBottomProtectionStandardDeviation" +
                 "AND NEW.FailureProbabilityOpenStructure IS OLD.FailureProbabilityOpenStructure" +
-                "AND NEW.IdenticalApertures IS OLD.IdenticalApertures" +
                 "AND NEW.FailureProbabilityReparation IS OLD.FailureProbabilityReparation" +
                 "AND NEW.InflowModelType IS OLD.InflowModelType;" +
                 "DETACH DATABASE SOURCEPROJECT;";