diff --git a/src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs b/src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs
index 67d5da7..c62a02e 100644
--- a/src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs
+++ b/src/ObservableCollections.R3/ObservableCollectionR3Extensions.cs
@@ -71,7 +71,7 @@ public static class ObservableCollectionR3Extensions
         return new ObservableCollectionReverse<T>(source, cancellationToken);
     }
 
-    public static Observable<(int Index, int Count, IComparer<T> Comparer)> ObserveSort<T>(this IObservableCollection<T> source, CancellationToken cancellationToken = default)
+    public static Observable<(int Index, int Count, IComparer<T>? Comparer)> ObserveSort<T>(this IObservableCollection<T> source, CancellationToken cancellationToken = default)
     {
         return new ObservableCollectionSort<T>(source, cancellationToken);
     }
@@ -290,18 +290,18 @@ sealed class ObservableCollectionReverse<T>(IObservableCollection<T> collection,
     }
 }
 
-sealed class ObservableCollectionSort<T>(IObservableCollection<T> collection, CancellationToken cancellationToken) : Observable<(int Index, int Count, IComparer<T> Comparer)>
+sealed class ObservableCollectionSort<T>(IObservableCollection<T> collection, CancellationToken cancellationToken) : Observable<(int Index, int Count, IComparer<T>? Comparer)>
 {
-    protected override IDisposable SubscribeCore(Observer<(int Index, int Count, IComparer<T> Comparer)> observer)
+    protected override IDisposable SubscribeCore(Observer<(int Index, int Count, IComparer<T>? Comparer)> observer)
     {
         return new _ObservableCollectionSort(collection, observer, cancellationToken);
     }
 
     sealed class _ObservableCollectionSort(
         IObservableCollection<T> collection,
-        Observer<(int Index, int Count, IComparer<T> Comparer)> observer,
+        Observer<(int Index, int Count, IComparer<T>? Comparer)> observer,
         CancellationToken cancellationToken)
-        : ObservableCollectionObserverBase<T, (int Index, int Count, IComparer<T> Comparer)>(collection, observer, cancellationToken)
+        : ObservableCollectionObserverBase<T, (int Index, int Count, IComparer<T>? Comparer)>(collection, observer, cancellationToken)
     {
         protected override void Handler(in NotifyCollectionChangedEventArgs<T> eventArgs)
         {
diff --git a/src/ObservableCollections/NotifyCollectionChangedEventArgs.cs b/src/ObservableCollections/NotifyCollectionChangedEventArgs.cs
index 790c606..22c149a 100644
--- a/src/ObservableCollections/NotifyCollectionChangedEventArgs.cs
+++ b/src/ObservableCollections/NotifyCollectionChangedEventArgs.cs
@@ -25,9 +25,9 @@ namespace ObservableCollections
             Comparer = comparer ?? NullComparerSentinel.Instance;
         }
 
-        public (int Index, int Count, IComparer<T> Comparer) AsTuple()
+        public (int Index, int Count, IComparer<T>? Comparer) AsTuple()
         {
-            return (Index, Count, Comparer!);
+            return (Index, Count, Comparer);
         }
 
         public static SortOperation<T> CreateReverse(int index, int count)