diff --git a/Remotion/Data/DomainObjects.UnitTests/ClientTransactionExtensionCollectionTest.cs b/Remotion/Data/DomainObjects.UnitTests/ClientTransactionExtensionCollectionTest.cs
index fe833df909..833baf1a86 100644
--- a/Remotion/Data/DomainObjects.UnitTests/ClientTransactionExtensionCollectionTest.cs
+++ b/Remotion/Data/DomainObjects.UnitTests/ClientTransactionExtensionCollectionTest.cs
@@ -15,6 +15,7 @@
 // along with re-motion; if not, see http://www.gnu.org/licenses.
 // 
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Diagnostics;
@@ -69,6 +70,39 @@ public void Initialization ()
       Assert.That(((IClientTransactionExtension)collection).Key, Is.EqualTo("abc"));
     }
 
+    [Test]
+    public void GetEnumerator_IEnumerableGeneric ()
+    {
+      _collection.Add(_extension1.Object);
+      _collection.Add(_extension2.Object);
+
+      using IEnumerator<IClientTransactionExtension> enumerator = ((IEnumerable<IClientTransactionExtension>)_collection).GetEnumerator();
+
+      Assert.That(enumerator.Current, Is.Null);
+      Assert.That(enumerator.MoveNext(), Is.True);
+      Assert.That(enumerator.Current, Is.EqualTo(_extension1.Object));
+      Assert.That(enumerator.MoveNext(), Is.True);
+      Assert.That(enumerator.Current, Is.EqualTo(_extension2.Object));
+      Assert.That(enumerator.MoveNext(), Is.False);
+    }
+
+    [Test]
+    public void GetEnumerator_ForIEnumerable ()
+    {
+      _collection.Add(_extension1.Object);
+      _collection.Add(_extension2.Object);
+
+      // ReSharper disable once NotDisposedResource
+      IEnumerator enumerator = ((IEnumerable)_collection).GetEnumerator();
+
+      Assert.That(enumerator.Current, Is.Null);
+      Assert.That(enumerator.MoveNext(), Is.True);
+      Assert.That(enumerator.Current, Is.EqualTo(_extension1.Object));
+      Assert.That(enumerator.MoveNext(), Is.True);
+      Assert.That(enumerator.Current, Is.EqualTo(_extension2.Object));
+      Assert.That(enumerator.MoveNext(), Is.False);
+    }
+
     [Test]
     public void Add ()
     {
@@ -95,10 +129,11 @@ public void Insert ()
     [Test]
     public void Remove ()
     {
+      _collection.Add(_extension2.Object);
       _collection.Add(_extension1.Object);
-      Assert.That(_collection.Count, Is.EqualTo(1));
+      Assert.That(_collection.Count, Is.EqualTo(2));
       _collection.Remove(_extension1.Object.Key);
-      Assert.That(_collection.Count, Is.EqualTo(0));
+      Assert.That(_collection.Count, Is.EqualTo(1));
       _collection.Remove(_extension1.Object.Key);
       //expectation: no exception
     }
@@ -113,12 +148,13 @@ public void Indexer ()
     }
 
     [Test]
-    public void IndexerWithName ()
+    public void IndexerWithKey ()
     {
       _collection.Add(_extension1.Object);
       _collection.Add(_extension2.Object);
       Assert.That(_collection[_extension1.Object.Key], Is.SameAs(_extension1.Object));
       Assert.That(_collection[_extension2.Object.Key], Is.SameAs(_extension2.Object));
+      Assert.That(_collection["unknown"], Is.Null);
     }
 
     [Test]
@@ -144,7 +180,7 @@ public void AddWithDuplicateKey ()
     }
 
     [Test]
-    public void InsertWithDuplicateName ()
+    public void InsertWithDuplicateKey ()
     {
       _collection.Insert(0, _extension1.Object);
 
diff --git a/Remotion/Data/DomainObjects/ClientTransactionExtensionCollection.cs b/Remotion/Data/DomainObjects/ClientTransactionExtensionCollection.cs
index d6c5d99a26..28c25e3231 100644
--- a/Remotion/Data/DomainObjects/ClientTransactionExtensionCollection.cs
+++ b/Remotion/Data/DomainObjects/ClientTransactionExtensionCollection.cs
@@ -15,6 +15,7 @@
 // along with re-motion; if not, see http://www.gnu.org/licenses.
 // 
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Linq;
@@ -30,9 +31,10 @@ namespace Remotion.Data.DomainObjects
   /// A collection of <see cref="IClientTransactionExtension"/>s.
   /// </summary>
   [Serializable]
-  public class ClientTransactionExtensionCollection : CommonCollection, IClientTransactionExtension
+  public class ClientTransactionExtensionCollection : IClientTransactionExtension, IReadOnlyList<IClientTransactionExtension>
   {
     private readonly string _key;
+    private readonly List<KeyValuePair<string, IClientTransactionExtension>> _extensions = new();
 
     public ClientTransactionExtensionCollection (string key)
     {
@@ -53,7 +55,7 @@ public IClientTransactionExtension? this[string key]
       {
         ArgumentUtility.CheckNotNullOrEmpty("key", key);
 
-        return (IClientTransactionExtension?)BaseGetObject(key);
+        return _extensions.FirstOrDefault(e => KeyPredicate(e, key)).Value;
       }
     }
 
@@ -64,7 +66,7 @@ public IClientTransactionExtension? this[string key]
     /// <returns>The <see cref="IClientTransactionExtension"/> of the given <paramref name="index"/>.</returns>
     public IClientTransactionExtension this[int index]
     {
-      get { return (IClientTransactionExtension)BaseGetObject(index); }
+      get { return _extensions[index].Value; }
     }
 
     string IClientTransactionExtension.Key
@@ -86,10 +88,10 @@ public void Add (IClientTransactionExtension clientTransactionExtension)
       var key = clientTransactionExtension.Key;
       Assertion.IsNotNull(key, "IClientTransactionExtension.Key must not return null");
 
-      if (BaseContainsKey(key))
+      if (_extensions.Any(e => KeyPredicate(e, key)))
         throw new InvalidOperationException(string.Format("An extension with key '{0}' is already part of the collection.", key));
 
-      BaseAdd(key, clientTransactionExtension);
+      _extensions.Add(new KeyValuePair<string, IClientTransactionExtension>(key, clientTransactionExtension));
     }
 
     /// <summary>
@@ -100,7 +102,7 @@ public void Remove (string key)
     {
       ArgumentUtility.CheckNotNullOrEmpty("key", key);
 
-      BaseRemove(key);
+      _extensions.RemoveAll(e => KeyPredicate(e, key));
     }
 
     /// <summary>
@@ -112,7 +114,7 @@ public int IndexOf (string key)
     {
       ArgumentUtility.CheckNotNullOrEmpty("key", key);
 
-      return BaseIndexOfKey(key);
+      return _extensions.FindIndex(e => KeyPredicate(e, key));
     }
 
     /// <summary>
@@ -130,12 +132,20 @@ public void Insert (int index, IClientTransactionExtension clientTransactionExte
       var key = clientTransactionExtension.Key;
       Assertion.IsNotNull(key, "IClientTransactionExtension.Key must not return null");
 
-      if (BaseContainsKey(key))
+      if (_extensions.Any(e => KeyPredicate(e, key)))
         throw new InvalidOperationException(string.Format("An extension with key '{0}' is already part of the collection.", key));
 
-      BaseInsert(index, key, clientTransactionExtension);
+      _extensions.Insert(index, new KeyValuePair<string, IClientTransactionExtension>(key, clientTransactionExtension));
     }
 
+    IEnumerator<IClientTransactionExtension> IEnumerable<IClientTransactionExtension>.GetEnumerator () => _extensions.Select(e => e.Value).GetEnumerator();
+
+    IEnumerator IEnumerable.GetEnumerator () => ((IEnumerable<IClientTransactionExtension>)this).GetEnumerator();
+
+    public int Count => _extensions.Count;
+
+    private static bool KeyPredicate (KeyValuePair<string, IClientTransactionExtension> extension, string key) => string.Equals(extension.Key, key, StringComparison.Ordinal);
+
     #region Notification methods
 
     [EditorBrowsable(EditorBrowsableState.Never)]
@@ -212,6 +222,7 @@ public void ObjectsLoaded (ClientTransaction clientTransaction, IReadOnlyList<Do
         this[i].ObjectsLoaded(clientTransaction, loadedDomainObjects);
     }
 
+    [EditorBrowsable(EditorBrowsableState.Never)]
     public void ObjectsUnloading (ClientTransaction clientTransaction, IReadOnlyList<DomainObject> unloadedDomainObjects)
     {
       ArgumentUtility.DebugCheckNotNull("unloadedDomainObjects", unloadedDomainObjects);
@@ -220,6 +231,7 @@ public void ObjectsUnloading (ClientTransaction clientTransaction, IReadOnlyList
         this[i].ObjectsUnloading(clientTransaction, unloadedDomainObjects);
     }
 
+    [EditorBrowsable(EditorBrowsableState.Never)]
     public void ObjectsUnloaded (ClientTransaction clientTransaction, IReadOnlyList<DomainObject> unloadedDomainObjects)
     {
       ArgumentUtility.DebugCheckNotNull("unloadedDomainObjects", unloadedDomainObjects);