diff --git a/src/ObservableCollections/ObservableDictionary.Views.cs b/src/ObservableCollections/ObservableDictionary.Views.cs
index ece0950..9ee370c 100644
--- a/src/ObservableCollections/ObservableDictionary.Views.cs
+++ b/src/ObservableCollections/ObservableDictionary.Views.cs
@@ -7,7 +7,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableDictionary<TKey, TValue>
+    public partial class ObservableDictionary<TKey, TValue>
     {
         public ISynchronizedView<KeyValuePair<TKey, TValue>, TView> CreateView<TView>(Func<KeyValuePair<TKey, TValue>, TView> transform)
         {
diff --git a/src/ObservableCollections/ObservableDictionary.cs b/src/ObservableCollections/ObservableDictionary.cs
index bb9e2f8..9d8b77a 100644
--- a/src/ObservableCollections/ObservableDictionary.cs
+++ b/src/ObservableCollections/ObservableDictionary.cs
@@ -7,7 +7,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableDictionary<TKey, TValue> : IDictionary<TKey, TValue>, IReadOnlyObservableDictionary<TKey, TValue>
+    public partial class ObservableDictionary<TKey, TValue> : IDictionary<TKey, TValue>, IReadOnlyObservableDictionary<TKey, TValue>
         where TKey : notnull
     {
         readonly Dictionary<TKey, TValue> dictionary;
diff --git a/src/ObservableCollections/ObservableFixedSizeRingBuffer.cs b/src/ObservableCollections/ObservableFixedSizeRingBuffer.cs
index 658a69c..0dc73ce 100644
--- a/src/ObservableCollections/ObservableFixedSizeRingBuffer.cs
+++ b/src/ObservableCollections/ObservableFixedSizeRingBuffer.cs
@@ -5,7 +5,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableFixedSizeRingBuffer<T> : IList<T>, IReadOnlyList<T>, IObservableCollection<T>
+    public partial class ObservableFixedSizeRingBuffer<T> : IList<T>, IReadOnlyList<T>, IObservableCollection<T>
     {
         readonly RingBuffer<T> buffer;
         readonly int capacity;
diff --git a/src/ObservableCollections/ObservableHashSet.Views.cs b/src/ObservableCollections/ObservableHashSet.Views.cs
index 50669d1..b355eaa 100644
--- a/src/ObservableCollections/ObservableHashSet.Views.cs
+++ b/src/ObservableCollections/ObservableHashSet.Views.cs
@@ -8,7 +8,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableHashSet<T> : IReadOnlyCollection<T>, IObservableCollection<T>
+    public partial class ObservableHashSet<T> : IReadOnlyCollection<T>, IObservableCollection<T>
     {
         public ISynchronizedView<T, TView> CreateView<TView>(Func<T, TView> transform)
         {
diff --git a/src/ObservableCollections/ObservableHashSet.cs b/src/ObservableCollections/ObservableHashSet.cs
index 0b95615..2534741 100644
--- a/src/ObservableCollections/ObservableHashSet.cs
+++ b/src/ObservableCollections/ObservableHashSet.cs
@@ -8,7 +8,7 @@
 namespace ObservableCollections
 {
     // can not implements ISet<T> because set operation can not get added/removed values.
-    public sealed partial class ObservableHashSet<T> : IReadOnlySet<T>, IReadOnlyCollection<T>, IObservableCollection<T>
+    public partial class ObservableHashSet<T> : IReadOnlySet<T>, IReadOnlyCollection<T>, IObservableCollection<T>
         where T : notnull
     {
         readonly HashSet<T> set;
diff --git a/src/ObservableCollections/ObservableList.OptimizeView.cs b/src/ObservableCollections/ObservableList.OptimizeView.cs
index c5052da..453b7c4 100644
--- a/src/ObservableCollections/ObservableList.OptimizeView.cs
+++ b/src/ObservableCollections/ObservableList.OptimizeView.cs
@@ -7,7 +7,7 @@
 
 namespace ObservableCollections;
 
-public sealed partial class ObservableList<T> : IList<T>, IReadOnlyObservableList<T>
+public partial class ObservableList<T> : IList<T>, IReadOnlyObservableList<T>
 {
     // override extension methods(IObservableCollection.cs ObservableCollectionExtensions)
 
diff --git a/src/ObservableCollections/ObservableList.Views.cs b/src/ObservableCollections/ObservableList.Views.cs
index 5eea0af..f4e35f2 100644
--- a/src/ObservableCollections/ObservableList.Views.cs
+++ b/src/ObservableCollections/ObservableList.Views.cs
@@ -7,7 +7,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableList<T> : IList<T>, IReadOnlyObservableList<T>
+    public partial class ObservableList<T> : IList<T>, IReadOnlyObservableList<T>
     {
         public ISynchronizedView<T, TView> CreateView<TView>(Func<T, TView> transform)
         {
diff --git a/src/ObservableCollections/ObservableList.cs b/src/ObservableCollections/ObservableList.cs
index 47a0d17..31c9294 100644
--- a/src/ObservableCollections/ObservableList.cs
+++ b/src/ObservableCollections/ObservableList.cs
@@ -7,7 +7,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableList<T> : IList<T>, IReadOnlyObservableList<T>
+    public partial class ObservableList<T> : IList<T>, IReadOnlyObservableList<T>
     {
         readonly List<T> list;
         public object SyncRoot { get; } = new();
diff --git a/src/ObservableCollections/ObservableQueue.Views.cs b/src/ObservableCollections/ObservableQueue.Views.cs
index e118dcf..b86af9d 100644
--- a/src/ObservableCollections/ObservableQueue.Views.cs
+++ b/src/ObservableCollections/ObservableQueue.Views.cs
@@ -8,7 +8,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableQueue<T> : IReadOnlyCollection<T>, IObservableCollection<T>
+    public partial class ObservableQueue<T> : IReadOnlyCollection<T>, IObservableCollection<T>
     {
         public ISynchronizedView<T, TView> CreateView<TView>(Func<T, TView> transform)
         {
diff --git a/src/ObservableCollections/ObservableQueue.cs b/src/ObservableCollections/ObservableQueue.cs
index db18b5b..fde7707 100644
--- a/src/ObservableCollections/ObservableQueue.cs
+++ b/src/ObservableCollections/ObservableQueue.cs
@@ -10,7 +10,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableQueue<T> : IReadOnlyCollection<T>, IObservableCollection<T>
+    public partial class ObservableQueue<T> : IReadOnlyCollection<T>, IObservableCollection<T>
     {
         readonly Queue<T> queue;
         public object SyncRoot { get; } = new object();
diff --git a/src/ObservableCollections/ObservableRingBuffer.Views.cs b/src/ObservableCollections/ObservableRingBuffer.Views.cs
index fed1f17..7cf58bd 100644
--- a/src/ObservableCollections/ObservableRingBuffer.Views.cs
+++ b/src/ObservableCollections/ObservableRingBuffer.Views.cs
@@ -8,7 +8,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableRingBuffer<T>
+    public partial class ObservableRingBuffer<T>
     {
         public ISynchronizedView<T, TView> CreateView<TView>(Func<T, TView> transform)
         {
diff --git a/src/ObservableCollections/ObservableRingBuffer.cs b/src/ObservableCollections/ObservableRingBuffer.cs
index 26976b9..c1b1825 100644
--- a/src/ObservableCollections/ObservableRingBuffer.cs
+++ b/src/ObservableCollections/ObservableRingBuffer.cs
@@ -6,7 +6,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableRingBuffer<T> : IList<T>, IReadOnlyList<T>, IObservableCollection<T>
+    public partial class ObservableRingBuffer<T> : IList<T>, IReadOnlyList<T>, IObservableCollection<T>
     {
         readonly RingBuffer<T> buffer;
 
diff --git a/src/ObservableCollections/ObservableStack.Views.cs b/src/ObservableCollections/ObservableStack.Views.cs
index 67b9bdb..b6206e4 100644
--- a/src/ObservableCollections/ObservableStack.Views.cs
+++ b/src/ObservableCollections/ObservableStack.Views.cs
@@ -7,7 +7,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableStack<T> : IReadOnlyCollection<T>, IObservableCollection<T>
+    public partial class ObservableStack<T> : IReadOnlyCollection<T>, IObservableCollection<T>
     {
         public ISynchronizedView<T, TView> CreateView<TView>(Func<T, TView> transform)
         {
diff --git a/src/ObservableCollections/ObservableStack.cs b/src/ObservableCollections/ObservableStack.cs
index 9103f00..78fea38 100644
--- a/src/ObservableCollections/ObservableStack.cs
+++ b/src/ObservableCollections/ObservableStack.cs
@@ -8,7 +8,7 @@
 
 namespace ObservableCollections
 {
-    public sealed partial class ObservableStack<T> : IReadOnlyCollection<T>, IObservableCollection<T>
+    public partial class ObservableStack<T> : IReadOnlyCollection<T>, IObservableCollection<T>
     {
         readonly Stack<T> stack;
         public object SyncRoot { get; } = new object();
diff --git a/src/ObservableCollections/RingBuffer.cs b/src/ObservableCollections/RingBuffer.cs
index 3d45700..9212e45 100644
--- a/src/ObservableCollections/RingBuffer.cs
+++ b/src/ObservableCollections/RingBuffer.cs
@@ -6,7 +6,7 @@
 
 namespace ObservableCollections
 {
-    public sealed class RingBuffer<T> : IList<T>, IReadOnlyList<T>
+    public class RingBuffer<T> : IList<T>, IReadOnlyList<T>
     {
         T[] buffer;
         int head;