diff --git a/sandbox/BlazorApp/BlazorApp.csproj b/sandbox/BlazorApp/BlazorApp.csproj
index e948168..e5eafff 100644
--- a/sandbox/BlazorApp/BlazorApp.csproj
+++ b/sandbox/BlazorApp/BlazorApp.csproj
@@ -4,4 +4,8 @@
     <TargetFramework>net6.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\ObservableCollections\ObservableCollections.csproj" />
+  </ItemGroup>
+
 </Project>
diff --git a/sandbox/BlazorApp/Pages/Index.razor b/sandbox/BlazorApp/Pages/Index.razor
index e54d914..1a6f6f4 100644
--- a/sandbox/BlazorApp/Pages/Index.razor
+++ b/sandbox/BlazorApp/Pages/Index.razor
@@ -1,7 +1,12 @@
 @page "/"
 
-<h1>Hello, world!</h1>
+<button @onclick=OnClick>button</button>
 
-Welcome to your new app.
-
-<SurveyPrompt Title="How is Blazor working for you?" />
+<table>
+	@foreach (var item in ItemsView)
+	{
+		<tr>
+			<td>@item</td>
+		</tr>
+	}
+</table>
\ No newline at end of file
diff --git a/sandbox/BlazorApp/Pages/Index.razor.cs b/sandbox/BlazorApp/Pages/Index.razor.cs
index c8a0fc1..45a68e3 100644
--- a/sandbox/BlazorApp/Pages/Index.razor.cs
+++ b/sandbox/BlazorApp/Pages/Index.razor.cs
@@ -1,9 +1,40 @@
 using Microsoft.AspNetCore.Components;
+using ObservableCollections;
 
 namespace BlazorApp.Pages;
 
 public partial class Index
 {
+    ObservableList<int> list;
+    public ISynchronizedView<int, int> ItemsView { get; set; }
+    int adder = 99;
 
 
+    RenderFragment fragment;
+
+    protected override void OnInitialized()
+    {
+        list = new ObservableList<int>();
+        list.AddRange(new[] { 1, 10, 188 });
+        ItemsView = list.CreateSortedView(x => x, x => x, comparer: Comparer<int>.Default).WithINotifyCollectionChanged();
+
+
+        fragment = builder =>
+        {
+            builder.GetFrames();
+
+        };
+    }
+
+    
+
+    void OnClick()
+    {
+        ThreadPool.QueueUserWorkItem(_ =>
+        {
+            list.Add(adder++);
+
+            _ = InvokeAsync(StateHasChanged);
+        });
+    }
 }
diff --git a/sandbox/WpfApp/MainWindow.xaml.cs b/sandbox/WpfApp/MainWindow.xaml.cs
index 38ab9bf..835e88d 100644
--- a/sandbox/WpfApp/MainWindow.xaml.cs
+++ b/sandbox/WpfApp/MainWindow.xaml.cs
@@ -30,7 +30,7 @@ namespace WpfApp
             InitializeComponent();
             this.DataContext = this;
 
-
+            
 
 
             list = new ObservableList<int>();
diff --git a/src/ObservableCollections/FreezedDictionary.cs b/src/ObservableCollections/FreezedDictionary.cs
index 4a80455..c973850 100644
--- a/src/ObservableCollections/FreezedDictionary.cs
+++ b/src/ObservableCollections/FreezedDictionary.cs
@@ -1,4 +1,6 @@
-using ObservableCollections.Internal;
+#nullable disable
+
+using ObservableCollections.Internal;
 using System;
 using System.Collections;
 using System.Collections.Generic;
diff --git a/src/ObservableCollections/IObservableCollection.cs b/src/ObservableCollections/IObservableCollection.cs
index d382fc8..ef21cac 100644
--- a/src/ObservableCollections/IObservableCollection.cs
+++ b/src/ObservableCollections/IObservableCollection.cs
@@ -1,4 +1,6 @@
 using ObservableCollections.Internal;
+using System;
+using System.Collections.Generic;
 using System.Collections.Specialized;
 using System.ComponentModel;
 
diff --git a/src/ObservableCollections/Internal/CloneCollection.cs b/src/ObservableCollections/Internal/CloneCollection.cs
index 7bfadc9..4e9268e 100644
--- a/src/ObservableCollections/Internal/CloneCollection.cs
+++ b/src/ObservableCollections/Internal/CloneCollection.cs
@@ -1,5 +1,7 @@
-using System.Buffers;
+using System;
+using System.Buffers;
 using System.Collections;
+using System.Collections.Generic;
 using System.Runtime.CompilerServices;
 
 namespace ObservableCollections.Internal
@@ -24,7 +26,7 @@ namespace ObservableCollections.Internal
 
         public CloneCollection(IEnumerable<T> source)
         {
-            if (Enumerable.TryGetNonEnumeratedCount(source, out var count))
+            if (source.TryGetNonEnumeratedCount(out var count))
             {
                 var array = ArrayPool<T>.Shared.Rent(count);
 
@@ -70,7 +72,7 @@ namespace ObservableCollections.Internal
         {
             if (array.Length == index)
             {
-                ArrayPool<T>.Shared.Return(array, RuntimeHelpers.IsReferenceOrContainsReferences<T>());
+                ArrayPool<T>.Shared.Return(array, RuntimeHelpersEx.IsReferenceOrContainsReferences<T>());
             }
             array = ArrayPool<T>.Shared.Rent(index * 2);
         }
@@ -79,7 +81,7 @@ namespace ObservableCollections.Internal
         {
             if (array != null)
             {
-                ArrayPool<T>.Shared.Return(array, RuntimeHelpers.IsReferenceOrContainsReferences<T>());
+                ArrayPool<T>.Shared.Return(array, RuntimeHelpersEx.IsReferenceOrContainsReferences<T>());
                 array = null;
             }
         }
diff --git a/src/ObservableCollections/Internal/ResizableArray.cs b/src/ObservableCollections/Internal/ResizableArray.cs
index c520fab..a999db0 100644
--- a/src/ObservableCollections/Internal/ResizableArray.cs
+++ b/src/ObservableCollections/Internal/ResizableArray.cs
@@ -1,4 +1,5 @@
-using System.Buffers;
+using System;
+using System.Buffers;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 
@@ -32,7 +33,7 @@ namespace ObservableCollections.Internal
         void EnsureCapacity()
         {
             var newArray = array.AsSpan().ToArray();
-            ArrayPool<T>.Shared.Return(array!, RuntimeHelpers.IsReferenceOrContainsReferences<T>());
+            ArrayPool<T>.Shared.Return(array!, RuntimeHelpersEx.IsReferenceOrContainsReferences<T>());
             array = newArray;
         }
 
@@ -40,7 +41,7 @@ namespace ObservableCollections.Internal
         {
             if (array != null)
             {
-                ArrayPool<T>.Shared.Return(array, RuntimeHelpers.IsReferenceOrContainsReferences<T>());
+                ArrayPool<T>.Shared.Return(array, RuntimeHelpersEx.IsReferenceOrContainsReferences<T>());
                 array = null;
             }
         }
diff --git a/src/ObservableCollections/Internal/SortedView.cs b/src/ObservableCollections/Internal/SortedView.cs
index 7dec6d8..7aaa6c8 100644
--- a/src/ObservableCollections/Internal/SortedView.cs
+++ b/src/ObservableCollections/Internal/SortedView.cs
@@ -1,5 +1,8 @@
-using System.Collections;
+using System;
+using System.Collections;
+using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Linq;
 
 namespace ObservableCollections.Internal
 {
diff --git a/src/ObservableCollections/Internal/SortedViewViewComparer.cs b/src/ObservableCollections/Internal/SortedViewViewComparer.cs
index b479017..b8aad3e 100644
--- a/src/ObservableCollections/Internal/SortedViewViewComparer.cs
+++ b/src/ObservableCollections/Internal/SortedViewViewComparer.cs
@@ -1,5 +1,8 @@
-using System.Collections;
+using System;
+using System.Collections;
+using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Linq;
 
 namespace ObservableCollections.Internal
 {
diff --git a/src/ObservableCollections/ObservableCollections.csproj b/src/ObservableCollections/ObservableCollections.csproj
index 58ef59a..496abf6 100644
--- a/src/ObservableCollections/ObservableCollections.csproj
+++ b/src/ObservableCollections/ObservableCollections.csproj
@@ -1,8 +1,13 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>net6.0</TargetFramework>
+        <TargetFrameworks>netstandard2.0;netstandard2.1;net5.0;net6.0</TargetFrameworks>
         <Nullable>enable</Nullable>
+        <LangVersion>10.0</LangVersion>
     </PropertyGroup>
 
+    <ItemGroup Condition="$(TargetFramework) == 'netstandard2.0'">
+        <PackageReference Include="System.Memory" Version="4.5.4" />
+    </ItemGroup>
+
 </Project>
diff --git a/src/ObservableCollections/ObservableDictionary.Views.cs b/src/ObservableCollections/ObservableDictionary.Views.cs
index 256fe08..2bee71e 100644
--- a/src/ObservableCollections/ObservableDictionary.Views.cs
+++ b/src/ObservableCollections/ObservableDictionary.Views.cs
@@ -1,6 +1,9 @@
 using ObservableCollections.Internal;
+using System;
 using System.Collections;
+using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Linq;
 
 namespace ObservableCollections
 {
diff --git a/src/ObservableCollections/ObservableDictionary.cs b/src/ObservableCollections/ObservableDictionary.cs
index 891988e..964d731 100644
--- a/src/ObservableCollections/ObservableDictionary.cs
+++ b/src/ObservableCollections/ObservableDictionary.cs
@@ -20,7 +20,15 @@ namespace ObservableCollections
 
         public ObservableDictionary(IEnumerable<KeyValuePair<TKey, TValue>> collection)
         {
+#if NET6_0_OR_GREATER
             this.dictionary = new Dictionary<TKey, TValue>(collection);
+#else
+            this.dictionary = new Dictionary<TKey, TValue>();
+            foreach (var item in collection)
+            {
+                dictionary.Add(item.Key, item.Value);
+            }
+#endif
         }
 
         public event NotifyCollectionChangedEventHandler<KeyValuePair<TKey, TValue>>? CollectionChanged;
@@ -191,7 +199,9 @@ namespace ObservableCollections
             }
         }
 
+#pragma warning disable CS8767
         public bool TryGetValue(TKey key, [MaybeNullWhen(false)] out TValue value)
+#pragma warning restore CS8767
         {
             lock (SyncRoot)
             {
diff --git a/src/ObservableCollections/ObservableFixedSizeRingBuffer.cs b/src/ObservableCollections/ObservableFixedSizeRingBuffer.cs
index a450564..d67a11c 100644
--- a/src/ObservableCollections/ObservableFixedSizeRingBuffer.cs
+++ b/src/ObservableCollections/ObservableFixedSizeRingBuffer.cs
@@ -1,5 +1,7 @@
 using ObservableCollections.Internal;
+using System;
 using System.Collections;
+using System.Collections.Generic;
 
 namespace ObservableCollections
 {
diff --git a/src/ObservableCollections/ObservableHashSet.Views.cs b/src/ObservableCollections/ObservableHashSet.Views.cs
index d362841..49450af 100644
--- a/src/ObservableCollections/ObservableHashSet.Views.cs
+++ b/src/ObservableCollections/ObservableHashSet.Views.cs
@@ -1,6 +1,9 @@
 using ObservableCollections.Internal;
 using System.Collections;
+using System.Collections.Generic;
 using System.Collections.Specialized;
+using System;
+using System.Linq;
 
 namespace ObservableCollections
 {
diff --git a/src/ObservableCollections/ObservableHashSet.cs b/src/ObservableCollections/ObservableHashSet.cs
index 736c6be..3183f0c 100644
--- a/src/ObservableCollections/ObservableHashSet.cs
+++ b/src/ObservableCollections/ObservableHashSet.cs
@@ -1,5 +1,7 @@
 using ObservableCollections.Internal;
+using System;
 using System.Collections;
+using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 
 namespace ObservableCollections
@@ -16,11 +18,15 @@ namespace ObservableCollections
             this.set = new HashSet<T>();
         }
 
+#if NETSTANDARD2_1_OR_GREATER || NET5_0_OR_GREATER
+
         public ObservableHashSet(int capacity)
         {
             this.set = new HashSet<T>(capacity);
         }
 
+#endif
+
         public ObservableHashSet(IEnumerable<T> collection)
         {
             this.set = new HashSet<T>(collection);
@@ -174,11 +180,15 @@ namespace ObservableCollections
             }
         }
 
+#if !NETSTANDARD2_0
+
         public bool TryGetValue(T equalValue, [MaybeNullWhen(false)] out T actualValue)
         {
             return set.TryGetValue(equalValue, out actualValue);
         }
 
+#endif
+
         public bool Contains(T item)
         {
             lock (SyncRoot)
diff --git a/src/ObservableCollections/ObservableList.Views.cs b/src/ObservableCollections/ObservableList.Views.cs
index 49e463c..0a503b6 100644
--- a/src/ObservableCollections/ObservableList.Views.cs
+++ b/src/ObservableCollections/ObservableList.Views.cs
@@ -1,6 +1,9 @@
 using ObservableCollections.Internal;
+using System;
 using System.Collections;
+using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Linq;
 
 namespace ObservableCollections
 {
diff --git a/src/ObservableCollections/ObservableList.cs b/src/ObservableCollections/ObservableList.cs
index 92ac0f8..f611db3 100644
--- a/src/ObservableCollections/ObservableList.cs
+++ b/src/ObservableCollections/ObservableList.cs
@@ -102,7 +102,6 @@ namespace ObservableCollections
             lock (SyncRoot)
             {
                 var index = list.Count;
-                list.EnsureCapacity(items.Length);
                 foreach (var item in items)
                 {
                     list.Add(item);
@@ -242,7 +241,11 @@ namespace ObservableCollections
         {
             lock (SyncRoot)
             {
+#if NET5_0_OR_GREATER
                 var range = CollectionsMarshal.AsSpan(list).Slice(index, count);
+#else
+                var range = list.GetRange(index, count);
+#endif
 
                 // require copy before remove
                 using (var xs = new CloneCollection<T>(range))
diff --git a/src/ObservableCollections/ObservableQueue.Views.cs b/src/ObservableCollections/ObservableQueue.Views.cs
index dc2ef59..82fc720 100644
--- a/src/ObservableCollections/ObservableQueue.Views.cs
+++ b/src/ObservableCollections/ObservableQueue.Views.cs
@@ -1,6 +1,9 @@
 using ObservableCollections.Internal;
 using System.Collections;
 using System.Collections.Specialized;
+using System;
+using System.Collections.Generic;
+using System.Linq;
 
 namespace ObservableCollections
 {
@@ -120,7 +123,6 @@ namespace ObservableCollections
                             }
                             else
                             {
-                                queue.EnsureCapacity(e.NewItems.Length);
                                 foreach (var item in e.NewItems)
                                 {
                                     var v = (item, selector(item));
diff --git a/src/ObservableCollections/ObservableQueue.cs b/src/ObservableCollections/ObservableQueue.cs
index 6696a6a..7de4d5f 100644
--- a/src/ObservableCollections/ObservableQueue.cs
+++ b/src/ObservableCollections/ObservableQueue.cs
@@ -3,6 +3,10 @@ using System.Buffers;
 using System.Collections;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
+using System;
+using System.Collections.Generic;
+using System.Collections.Specialized;
+using System.Linq;
 
 namespace ObservableCollections
 {
@@ -105,11 +109,13 @@ namespace ObservableCollections
         {
             lock (SyncRoot)
             {
-                if (queue.TryDequeue(out result))
+                if (queue.Count != 0)
                 {
+                    result = queue.Dequeue();
                     CollectionChanged?.Invoke(NotifyCollectionChangedEventArgs<T>.Remove(result, 0));
                     return true;
                 }
+                result = default;
                 return false;
             }
         }
@@ -130,7 +136,7 @@ namespace ObservableCollections
                 }
                 finally
                 {
-                    ArrayPool<T>.Shared.Return(dest, RuntimeHelpers.IsReferenceOrContainsReferences<T>());
+                    ArrayPool<T>.Shared.Return(dest, RuntimeHelpersEx.IsReferenceOrContainsReferences<T>());
                 }
             }
         }
@@ -169,7 +175,13 @@ namespace ObservableCollections
         {
             lock (SyncRoot)
             {
-                return queue.TryPeek(out result);
+                if (queue.Count != 0)
+                {
+                    result = queue.Peek();
+                    return true;
+                }
+                result = default;
+                return false;
             }
         }
 
@@ -189,14 +201,6 @@ namespace ObservableCollections
             }
         }
 
-        public void EnsureCapacity(int capacity)
-        {
-            lock (SyncRoot)
-            {
-                queue.EnsureCapacity(capacity);
-            }
-        }
-
         public IEnumerator<T> GetEnumerator()
         {
             return new SynchronizedEnumerator<T>(SyncRoot, queue.GetEnumerator());
diff --git a/src/ObservableCollections/ObservableRingBuffer.Views.cs b/src/ObservableCollections/ObservableRingBuffer.Views.cs
index aa7fc94..50df81e 100644
--- a/src/ObservableCollections/ObservableRingBuffer.Views.cs
+++ b/src/ObservableCollections/ObservableRingBuffer.Views.cs
@@ -1,6 +1,9 @@
 using ObservableCollections.Internal;
+using System;
 using System.Collections;
+using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Linq;
 
 namespace ObservableCollections
 {
diff --git a/src/ObservableCollections/ObservableRingBuffer.cs b/src/ObservableCollections/ObservableRingBuffer.cs
index c59ab83..0f653e3 100644
--- a/src/ObservableCollections/ObservableRingBuffer.cs
+++ b/src/ObservableCollections/ObservableRingBuffer.cs
@@ -1,4 +1,7 @@
 using ObservableCollections.Internal;
+using System;
+using System.Linq;
+using System.Collections.Generic;
 using System.Collections;
 
 namespace ObservableCollections
diff --git a/src/ObservableCollections/ObservableStack.Views.cs b/src/ObservableCollections/ObservableStack.Views.cs
index 3a3d4ef..81cbf97 100644
--- a/src/ObservableCollections/ObservableStack.Views.cs
+++ b/src/ObservableCollections/ObservableStack.Views.cs
@@ -1,6 +1,9 @@
 using ObservableCollections.Internal;
+using System;
 using System.Collections;
+using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Linq;
 
 namespace ObservableCollections
 {
@@ -120,7 +123,6 @@ namespace ObservableCollections
                             }
                             else
                             {
-                                stack.EnsureCapacity(e.NewItems.Length);
                                 foreach (var item in e.NewItems)
                                 {
                                     var v = (item, selector(item));
diff --git a/src/ObservableCollections/ObservableStack.cs b/src/ObservableCollections/ObservableStack.cs
index 2de5999..e1d56e7 100644
--- a/src/ObservableCollections/ObservableStack.cs
+++ b/src/ObservableCollections/ObservableStack.cs
@@ -1,6 +1,8 @@
 using ObservableCollections.Internal;
+using System;
 using System.Buffers;
 using System.Collections;
+using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 
@@ -102,11 +104,14 @@ namespace ObservableCollections
         {
             lock (SyncRoot)
             {
-                if (stack.TryPop(out result))
+                if (stack.Count != 0)
                 {
+                    result = stack.Pop();
                     CollectionChanged?.Invoke(NotifyCollectionChangedEventArgs<T>.Remove(result, 0));
                     return true;
                 }
+
+                result = default;
                 return false;
             }
         }
@@ -127,7 +132,7 @@ namespace ObservableCollections
                 }
                 finally
                 {
-                    ArrayPool<T>.Shared.Return(dest, RuntimeHelpers.IsReferenceOrContainsReferences<T>());
+                    ArrayPool<T>.Shared.Return(dest, RuntimeHelpersEx.IsReferenceOrContainsReferences<T>());
                 }
             }
         }
@@ -166,7 +171,13 @@ namespace ObservableCollections
         {
             lock (SyncRoot)
             {
-                return stack.TryPeek(out result);
+                if (stack.Count != 0)
+                {
+                    result = stack.Peek();
+                    return true;
+                }
+                result = default;
+                return false;
             }
         }
 
@@ -186,14 +197,6 @@ namespace ObservableCollections
             }
         }
 
-        public void EnsureCapacity(int capacity)
-        {
-            lock (SyncRoot)
-            {
-                stack.EnsureCapacity(capacity);
-            }
-        }
-
         public IEnumerator<T> GetEnumerator()
         {
             return new SynchronizedEnumerator<T>(SyncRoot, stack.GetEnumerator());
diff --git a/src/ObservableCollections/RingBuffer.cs b/src/ObservableCollections/RingBuffer.cs
index 5ba6d0d..a4d24dd 100644
--- a/src/ObservableCollections/RingBuffer.cs
+++ b/src/ObservableCollections/RingBuffer.cs
@@ -1,4 +1,6 @@
-using System.Collections;
+using System;
+using System.Collections;
+using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 
 namespace ObservableCollections
@@ -147,7 +149,7 @@ namespace ObservableCollections
 
         public void Clear()
         {
-            Array.Clear(buffer);
+            Array.Clear(buffer, 0, buffer.Length);
             head = 0;
             count = 0;
         }
diff --git a/src/ObservableCollections/Shims/Collections.cs b/src/ObservableCollections/Shims/Collections.cs
new file mode 100644
index 0000000..d20c328
--- /dev/null
+++ b/src/ObservableCollections/Shims/Collections.cs
@@ -0,0 +1,64 @@
+#nullable disable
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace System.Collections.Generic
+{
+    internal static class CollectionExtensions
+    {
+        public static void Deconstruct<TKey, TValue>(this KeyValuePair<TKey, TValue> kvp, out TKey key, out TValue value)
+        {
+            key = kvp.Key;
+            value = kvp.Value;
+        }
+
+        public static bool Remove<TKey, TValue>(this SortedDictionary<TKey, TValue> dict, TKey key, out TValue value)
+        {
+            if (dict.TryGetValue(key, out value))
+            {
+                return dict.Remove(key);
+            }
+            return false;
+        }
+
+        public static bool Remove<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key, out TValue value)
+        {
+            if (dict.TryGetValue(key, out value))
+            {
+                return dict.Remove(key);
+            }
+            return false;
+        }
+
+#if !NET6_0_OR_GREATER
+
+        public static bool TryGetNonEnumeratedCount<T>(this IEnumerable<T> source, out int count)
+        {
+            if (source is ICollection<T> collection)
+            {
+                count = collection.Count;
+                return true;
+            }
+            if (source is IReadOnlyCollection<T> rCollection)
+            {
+                count = rCollection.Count;
+                return true;
+            }
+            count = 0;
+            return false;
+        }
+
+#endif
+    }
+
+#if !NET5_0_OR_GREATER
+
+    internal interface IReadOnlySet<T> : System.Collections.Generic.IEnumerable<T>, System.Collections.Generic.IReadOnlyCollection<T>
+    {
+    }
+
+#endif
+}
+
diff --git a/src/ObservableCollections/Shims/CompilerServices.cs b/src/ObservableCollections/Shims/CompilerServices.cs
new file mode 100644
index 0000000..07826dc
--- /dev/null
+++ b/src/ObservableCollections/Shims/CompilerServices.cs
@@ -0,0 +1,18 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace System.Runtime.CompilerServices
+{
+    internal static class RuntimeHelpersEx
+    {
+        internal static bool IsReferenceOrContainsReferences<T>()
+        {
+#if NETSTANDARD2_0
+            return true;
+#else
+            return RuntimeHelpers.IsReferenceOrContainsReferences<T>();
+#endif
+        }
+    }
+}
diff --git a/src/ObservableCollections/Shims/Nullables.cs b/src/ObservableCollections/Shims/Nullables.cs
new file mode 100644
index 0000000..3e96443
--- /dev/null
+++ b/src/ObservableCollections/Shims/Nullables.cs
@@ -0,0 +1,24 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+#if NETSTANDARD2_0
+
+namespace System.Diagnostics.CodeAnalysis
+{
+    internal sealed class MaybeNullWhenAttribute : Attribute
+    {
+        public MaybeNullWhenAttribute(bool returnValue)
+        {
+        }
+    }
+
+    internal sealed class DoesNotReturnAttribute : Attribute
+    {
+        public DoesNotReturnAttribute()
+        {
+        }
+    }
+}
+
+#endif
\ No newline at end of file