diff --git a/SysML2.NET.Tests/Extend/ClassifierExtensionsTestFixture.cs b/SysML2.NET.Tests/Extend/ClassifierExtensionsTestFixture.cs
index e77764c6..b2d62527 100644
--- a/SysML2.NET.Tests/Extend/ClassifierExtensionsTestFixture.cs
+++ b/SysML2.NET.Tests/Extend/ClassifierExtensionsTestFixture.cs
@@ -1,7 +1,7 @@
 // -------------------------------------------------------------------------------------------------
 // <copyright file="ClassifierExtensionsTestFixture.cs" company="Starion Group S.A.">
 // 
-//   Copyright 2022-2026 Starion Group S.A.
+//   Copyright (C) 2022-2026 Starion Group S.A.
 // 
 //   Licensed under the Apache License, Version 2.0 (the "License");
 //   you may not use this file except in compliance with the License.
@@ -21,18 +21,38 @@
 namespace SysML2.NET.Tests.Extend
 {
     using System;
-    
+
     using NUnit.Framework;
 
     using SysML2.NET.Core.POCO.Core.Classifiers;
+    using SysML2.NET.Core.POCO.Core.Types;
+    using SysML2.NET.Extensions;
 
     [TestFixture]
     public class ClassifierExtensionsTestFixture
     {
         [Test]
-        public void ComputeOwnedSubclassification_ThrowsNotSupportedException()
+        public void VerifyComputeOwnedSubclassification()
         {
-            Assert.That(() => ((IClassifier)null).ComputeOwnedSubclassification(), Throws.TypeOf<NotSupportedException>());
+            // Null subject:
+            Assert.That(() => ((IClassifier)null).ComputeOwnedSubclassification(), Throws.TypeOf<ArgumentNullException>());
+
+            // Empty classifier:
+            var subject = new Classifier();
+            Assert.That(subject.ComputeOwnedSubclassification(), Has.Count.EqualTo(0));
+
+            var superClassifier = new Classifier();
+
+            var subclassification = new Subclassification
+            {
+                Subclassifier = subject,
+                Superclassifier = superClassifier
+            };
+
+            subject.AssignOwnership(subclassification);
+
+            Assert.That(subject.ComputeOwnedSubclassification(), Is.EquivalentTo([subclassification]));
+
         }
     }
 }
diff --git a/SysML2.NET/Extend/ClassifierExtensions.cs b/SysML2.NET/Extend/ClassifierExtensions.cs
index cef3bc35..0ab4c593 100644
--- a/SysML2.NET/Extend/ClassifierExtensions.cs
+++ b/SysML2.NET/Extend/ClassifierExtensions.cs
@@ -1,20 +1,20 @@
 // -------------------------------------------------------------------------------------------------
 // <copyright file="ClassifierExtensions.cs" company="Starion Group S.A.">
-//
-//    Copyright (C) 2022-2026 Starion Group S.A.
-//
-//    Licensed under the Apache License, Version 2.0 (the "License");
-//    you may not use this file except in compliance with the License.
-//    You may obtain a copy of the License at
-//
+// 
+//   Copyright (C) 2022-2026 Starion Group S.A.
+// 
+//   Licensed under the Apache License, Version 2.0 (the "License");
+//   you may not use this file except in compliance with the License.
+//   You may obtain a copy of the License at
+// 
 //        http://www.apache.org/licenses/LICENSE-2.0
-//
+// 
 //    Unless required by applicable law or agreed to in writing, software
 //    distributed under the License is distributed on an "AS IS" BASIS,
 //    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 //    See the License for the specific language governing permissions and
 //    limitations under the License.
-//
+// 
 // </copyright>
 // ------------------------------------------------------------------------------------------------
 
@@ -22,18 +22,11 @@ namespace SysML2.NET.Core.POCO.Core.Classifiers
 {
     using System;
     using System.Collections.Generic;
-
-    using SysML2.NET.Core.Core.Types;
-    using SysML2.NET.Core.Root.Namespaces;
-    using SysML2.NET.Core.POCO.Core.Features;
-    using SysML2.NET.Core.POCO.Core.Types;
-    using SysML2.NET.Core.POCO.Root.Annotations;
-    using SysML2.NET.Core.POCO.Root.Elements;
-    using SysML2.NET.Core.POCO.Root.Namespaces;
+    using System.Linq;
 
     /// <summary>
-    /// The <see cref="ClassifierExtensions"/> class provides extensions methods for
-    /// the <see cref="IClassifier"/> interface
+    /// The <see cref="ClassifierExtensions" /> class provides extensions methods for
+    /// the <see cref="IClassifier" /> interface
     /// </summary>
     internal static class ClassifierExtensions
     {
@@ -48,16 +41,16 @@ internal static class ClassifierExtensions
         /// </code>
         /// </remarks>
         /// <param name="classifierSubject">
-        /// The subject <see cref="IClassifier"/>
+        /// The subject <see cref="IClassifier" />
         /// </param>
         /// <returns>
         /// the computed result
         /// </returns>
-        [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
         internal static List<ISubclassification> ComputeOwnedSubclassification(this IClassifier classifierSubject)
         {
-            throw new NotSupportedException("Create a GitHub issue when this method is required");
+            return classifierSubject == null
+                ? throw new ArgumentNullException(nameof(classifierSubject))
+                : [..classifierSubject.ownedSpecialization.OfType<ISubclassification>()];
         }
-
     }
 }