Index: Ringtoets/Migration/src/Ringtoets.Migration.Core/EmbeddedResources/Migration_17.3_18.1.sql
===================================================================
diff -u -r9f9450c0a749329d2fc88423e1038de599b890b1 -r623a4788917a79f7a28b13ae46d4d8cc6515b155
--- Ringtoets/Migration/src/Ringtoets.Migration.Core/EmbeddedResources/Migration_17.3_18.1.sql	(.../Migration_17.3_18.1.sql)	(revision 9f9450c0a749329d2fc88423e1038de599b890b1)
+++ Ringtoets/Migration/src/Ringtoets.Migration.Core/EmbeddedResources/Migration_17.3_18.1.sql	(.../Migration_17.3_18.1.sql)	(revision 623a4788917a79f7a28b13ae46d4d8cc6515b155)
@@ -77,7 +77,7 @@
 	END,
 	[FailureProbabilityOpenStructure],
 	CASE
-		WHEN [IdenticalApertures] = 0
+		WHEN [IdenticalApertures] < 1
 			THEN 1
 		ELSE 
 			[IdenticalApertures]
@@ -166,7 +166,7 @@
 	[ProbabilityOrFrequencyOpenStructureBeforeFlooding],
 	[FailureProbabilityOpenStructure],
 	CASE
-		WHEN [IdenticalApertures] = 0
+		WHEN [IdenticalApertures] < 1
 			THEN 1
 		ELSE 
 			[IdenticalApertures]
Index: Ringtoets/Migration/test/Ringtoets.Migration.Core.Test/test-data/MigrationTestProject173.rtd
===================================================================
diff -u -ra7d7482b8e6bad505902bbb3bd6f500c036e974c -r623a4788917a79f7a28b13ae46d4d8cc6515b155
Binary files differ
Index: Ringtoets/Migration/test/Ringtoets.Migration.Integration.Test/MigrationTo181IntegrationTest.cs
===================================================================
diff -u -rbd1ab7a1865194093b31787cd04c33aa71def5b7 -r623a4788917a79f7a28b13ae46d4d8cc6515b155
--- Ringtoets/Migration/test/Ringtoets.Migration.Integration.Test/MigrationTo181IntegrationTest.cs	(.../MigrationTo181IntegrationTest.cs)	(revision bd1ab7a1865194093b31787cd04c33aa71def5b7)
+++ Ringtoets/Migration/test/Ringtoets.Migration.Integration.Test/MigrationTo181IntegrationTest.cs	(.../MigrationTo181IntegrationTest.cs)	(revision 623a4788917a79f7a28b13ae46d4d8cc6515b155)
@@ -170,7 +170,7 @@
                 "SELECT " +
                 "CASE WHEN (NEW.[IdenticalApertures] != OLD.[IdenticalApertures] " +
                 "AND OLD.[IdenticalApertures] >= 1)  " +
-                "OR (NEW.[IdenticalApertures] != 1 AND OLD.[IdenticalApertures] = 0) " +
+                "OR (NEW.[IdenticalApertures] != 1 AND OLD.[IdenticalApertures] < 1) " +
                 "THEN 1 " +
                 "ELSE 0 " +
                 "END AS [IsInvalid] " +
@@ -227,7 +227,7 @@
                 "SELECT " +
                 "CASE WHEN (NEW.[IdenticalApertures] != OLD.[IdenticalApertures] " +
                 "AND OLD.[IdenticalApertures] >= 1)  " +
-                "OR (NEW.[IdenticalApertures] != 1 AND OLD.[IdenticalApertures] = 0) " +
+                "OR (NEW.[IdenticalApertures] != 1 AND OLD.[IdenticalApertures] < 1) " +
                 "THEN 1 " +
                 "ELSE 0 " +
                 "END AS [IsInvalid] " +
@@ -512,7 +512,7 @@
             {
                 ReadOnlyCollection<MigrationLogMessage> messages = reader.GetMigrationLogMessages();
 
-                Assert.AreEqual(70, messages.Count);
+                Assert.AreEqual(72, messages.Count);
                 var i = 0;
                 MigrationLogTestHelper.AssertMigrationLogMessageEqual(
                     new MigrationLogMessage("17.3", newVersion, "Gevolgen van de migratie van versie 17.3 naar versie 18.1:"),
@@ -741,6 +741,12 @@
                     new MigrationLogMessage("17.3", newVersion, "  + Toetsspoor: 'Betrouwbaarheid sluiting kunstwerk'"),
                     messages[i++]);
                 MigrationLogTestHelper.AssertMigrationLogMessageEqual(
+                    new MigrationLogMessage("17.3", newVersion, "    - De waarde van '-11' van parameter 'Aantal identieke doorstroomopeningen' van berekening 'Invalid Identical Apertures - Negative Value' is ongeldig en is veranderd naar 1."),
+                    messages[i++]);
+                MigrationLogTestHelper.AssertMigrationLogMessageEqual(
+                    new MigrationLogMessage("17.3", newVersion, "    - De waarde van '-11' van parameter 'Aantal identieke doorstroomopeningen' van kunstwerk 'Gemaal Leemans (Negatieve doorstroomopeningen)' is ongeldig en is veranderd naar 1."),
+                    messages[i++]);
+                MigrationLogTestHelper.AssertMigrationLogMessageEqual(
                     new MigrationLogMessage("17.3", newVersion, "    - De waarde van '0' van parameter 'Aantal identieke doorstroomopeningen' van berekening 'Invalid Identical Apertures' is ongeldig en is veranderd naar 1."),
                     messages[i++]);
                 MigrationLogTestHelper.AssertMigrationLogMessageEqual(