diff --git a/CHANGELOG.md b/CHANGELOG.md
index 65a407f7d0..9f0bf1c0d4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [9.2.0] - Unreleased
 - Add Internal Note to Catalogue
+- Fix issue with using Internal Catalogues in Cohort Identification Configurations
 
 ## [9.1.2] - Unreleased
 - Automatically fetch user settings from previous versions of RDMP when installing the latest version
diff --git a/Rdmp.Core.Tests/CohortCreation/CohortCompilerTests.cs b/Rdmp.Core.Tests/CohortCreation/CohortCompilerTests.cs
index 48d582cf81..001d2a7cd3 100644
--- a/Rdmp.Core.Tests/CohortCreation/CohortCompilerTests.cs
+++ b/Rdmp.Core.Tests/CohortCreation/CohortCompilerTests.cs
@@ -197,4 +197,24 @@ public void TestCompilerAddAllTasks(TestCompilerAddAllTasksTestCase testCase, bo
             aggregate5.DeleteInDatabase();
         }
     }
+
+    [Test]
+    public void TestCompilerWithInternalCatalogues()
+    {
+        var compiler = new CohortCompiler(cohortIdentificationConfiguration);
+        testData.catalogue.IsInternalDataset = true;
+        testData.catalogue.SaveToDatabase();
+
+        rootcontainer.AddChild(aggregate1, 1);
+        rootcontainer.AddChild(container1);
+        container1.Order = 2;
+        container1.SaveToDatabase();
+
+        cohortIdentificationConfiguration.RootCohortAggregateContainer_ID = rootcontainer.ID;
+        cohortIdentificationConfiguration.SaveToDatabase();
+
+        compiler.AddAllTasks(true);
+        Assert.That(compiler.Tasks.Keys.Select(k => k.State).Where(s => s == CompilationState.Crashed).ToList(), Has.Count.EqualTo(3));
+        Assert.That(compiler.Tasks.Keys.Where(s => s.State == CompilationState.Crashed).Select(k => k.CrashMessage.Message).ToList().Any(m => m.Contains(" is marked as Internal. Internal Catalogues cannot be used in Cohort Identification Configurations.")));
+    }
 }
\ No newline at end of file
diff --git a/Rdmp.Core/CohortCreation/Execution/CohortCompiler.cs b/Rdmp.Core/CohortCreation/Execution/CohortCompiler.cs
index a1f92685de..f78d2b065c 100644
--- a/Rdmp.Core/CohortCreation/Execution/CohortCompiler.cs
+++ b/Rdmp.Core/CohortCreation/Execution/CohortCompiler.cs
@@ -320,6 +320,28 @@ public ICompileable AddTask(IMapsDirectlyToDatabaseTable runnable, ISqlParameter
             task.State = CompilationState.Crashed;
         }
 
+        if(task.Child is CohortAggregateContainer cac)
+        {
+            foreach (var cacac in cac.GetAggregateConfigurations())
+            {
+                if (cacac.Catalogue != null && cacac.Catalogue.IsInternalDataset)
+                {
+                    task.CrashMessage = new ArgumentException($"Catalogue {cacac.Catalogue.Name} is marked as Internal. Internal Catalogues cannot be used in Cohort Identification Configurations.");
+                    task.State = CompilationState.Crashed;
+                    break;
+                }
+            }
+        }
+
+        if (task.Child is AggregateConfiguration ac)
+        {
+            if (ac.Catalogue != null && ac.Catalogue.IsInternalDataset)
+            {
+                task.CrashMessage = new ArgumentException($"Catalogue {ac.Catalogue.Name} is marked as Internal. Internal Catalogues cannot be used in Cohort Identification Configurations.");
+                task.State = CompilationState.Crashed;
+            }
+        }
+
         task.Log = queryBuilder?.Results?.Log;
 
 
diff --git a/Rdmp.Core/CommandExecution/AtomicCommands/ExecuteCommandAddCatalogueToCohortIdentificationSetContainer.cs b/Rdmp.Core/CommandExecution/AtomicCommands/ExecuteCommandAddCatalogueToCohortIdentificationSetContainer.cs
index 114cd2974e..97bb8a6219 100644
--- a/Rdmp.Core/CommandExecution/AtomicCommands/ExecuteCommandAddCatalogueToCohortIdentificationSetContainer.cs
+++ b/Rdmp.Core/CommandExecution/AtomicCommands/ExecuteCommandAddCatalogueToCohortIdentificationSetContainer.cs
@@ -58,6 +58,12 @@ public ExecuteCommandAddCatalogueToCohortIdentificationSetContainer(IBasicActiva
         {
             _catalogueCombineable = new CatalogueCombineable(catalogue);
 
+            if(catalogue.IsInternalDataset)
+            {
+                SetImpossible($"Catalogue '{catalogue}' is an Internal dataset and cannot be added to a Cohort Identification Set Container");
+                return;
+            }
+
             if (identifierColumn != null)
             {
                 if (!identifierColumn.IsExtractionIdentifier)
diff --git a/Rdmp.UI/CommandExecution/Proposals/ProposeExecutionWhenTargetIsAggregateConfiguration.cs b/Rdmp.UI/CommandExecution/Proposals/ProposeExecutionWhenTargetIsAggregateConfiguration.cs
index fe16f2a209..f28c1d401c 100644
--- a/Rdmp.UI/CommandExecution/Proposals/ProposeExecutionWhenTargetIsAggregateConfiguration.cs
+++ b/Rdmp.UI/CommandExecution/Proposals/ProposeExecutionWhenTargetIsAggregateConfiguration.cs
@@ -8,6 +8,7 @@
 using Rdmp.Core.CommandExecution.AtomicCommands;
 using Rdmp.Core.CommandExecution.Combining;
 using Rdmp.Core.Curation.Data.Aggregation;
+using Rdmp.Core.Curation.Data.Cohort;
 using Rdmp.UI.AggregationUIs.Advanced;
 using Rdmp.UI.CommandExecution.AtomicCommands;
 using Rdmp.UI.ItemActivation;
@@ -55,6 +56,7 @@ public override ICommandExecution ProposeExecution(ICombineToMakeCommand cmd,
                 BasedOn = efps.ParameterSet.ExtractionFilter,
                 ParameterSet = efps.ParameterSet
             },
+            CatalogueCombineable catalogueCombineable => new ExecuteCommandAddCatalogueToCohortIdentificationSetContainer(ItemActivator,targetAggregateConfiguration.GetCohortAggregateContainerIfAny(),catalogueCombineable.Catalogue),
             _ => null
         };
     }
diff --git a/Rdmp.UI/CommandExecution/Proposals/ProposeExecutionWhenTargetIsCohortAggregateContainer.cs b/Rdmp.UI/CommandExecution/Proposals/ProposeExecutionWhenTargetIsCohortAggregateContainer.cs
index 9bc5dff18c..aade7ff557 100644
--- a/Rdmp.UI/CommandExecution/Proposals/ProposeExecutionWhenTargetIsCohortAggregateContainer.cs
+++ b/Rdmp.UI/CommandExecution/Proposals/ProposeExecutionWhenTargetIsCohortAggregateContainer.cs
@@ -43,6 +43,7 @@ public override ICommandExecution ProposeExecution(ICombineToMakeCommand cmd,
             //source is catalogue
             case CatalogueCombineable sourceCatalogueCombineable:
                 {
+                    if (sourceCatalogueCombineable.Catalogue.IsInternalDataset) return null;
                     if (sourceCatalogueCombineable.Catalogue.IsProjectSpecific(ItemActivator.RepositoryLocator.DataExportRepository))
                     {
                         var dx = (DataExportChildProvider)ItemActivator.CoreChildProvider;