diff --git a/Avalonia.sln b/Avalonia.sln
index c000f56d09..461de8530b 100644
--- a/Avalonia.sln
+++ b/Avalonia.sln
@@ -41,6 +41,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Shared", "Shared", "{A689DE
 		src\Shared\IsExternalInit.cs = src\Shared\IsExternalInit.cs
 		src\Shared\ModuleInitializer.cs = src\Shared\ModuleInitializer.cs
 		src\Shared\SourceGeneratorAttributes.cs = src\Shared\SourceGeneratorAttributes.cs
+		src\Avalonia.Base\Compatibility\StringCompatibilityExtensions.cs = src\Avalonia.Base\Compatibility\StringCompatibilityExtensions.cs
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Avalonia.ReactiveUI", "src\Avalonia.ReactiveUI\Avalonia.ReactiveUI.csproj", "{6417B24E-49C2-4985-8DB2-3AB9D898EC91}"
diff --git a/src/Avalonia.Base/Avalonia.Base.csproj b/src/Avalonia.Base/Avalonia.Base.csproj
index 402bc3a099..bdb5882ef2 100644
--- a/src/Avalonia.Base/Avalonia.Base.csproj
+++ b/src/Avalonia.Base/Avalonia.Base.csproj
@@ -23,6 +23,7 @@
   <Import Project="..\..\build\SourceGenerators.props" />
   <ItemGroup>
     <Compile Include="..\Shared\IsExternalInit.cs" Link="IsExternalInit.cs" />
+    <Compile Include="..\Shared\StringCompatibilityExtensions.cs" Link="Compatibility\StringCompatibilityExtensions.cs" />
   </ItemGroup>
 
   <ItemGroup Label="InternalsVisibleTo">
@@ -46,6 +47,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <Folder Include="Compatibility\" />
     <Folder Include="Rendering\Composition\Utils" />
   </ItemGroup>
 </Project>
diff --git a/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj b/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj
index d0c39f0289..75746273c2 100644
--- a/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj
+++ b/src/Markup/Avalonia.Markup.Xaml/Avalonia.Markup.Xaml.csproj
@@ -9,6 +9,7 @@
     <NoWarn>CS1591</NoWarn>
   </PropertyGroup>
     <ItemGroup>
+        <Compile Include="..\..\Shared\StringCompatibilityExtensions.cs" Link="Compatibility\StringCompatibilityExtensions.cs" />
         <Compile Include="AvaloniaXamlLoader.cs" />
         <Compile Include="Converters\AvaloniaUriTypeConverter.cs" />
         <Compile Include="Converters\ColorToBrushConverter.cs" />
@@ -68,4 +69,8 @@
   <ItemGroup Label="InternalsVisibleTo">
     <InternalsVisibleTo Include="Avalonia.Markup.Xaml.UnitTests, PublicKey=$(AvaloniaPublicKey)" />
   </ItemGroup>
+
+  <ItemGroup>
+    <Folder Include="Compatibility\" />
+  </ItemGroup>
 </Project>
diff --git a/src/Avalonia.Base/Compatibility/StringCompatibilityExtensions.cs b/src/Shared/StringCompatibilityExtensions.cs
similarity index 83%
rename from src/Avalonia.Base/Compatibility/StringCompatibilityExtensions.cs
rename to src/Shared/StringCompatibilityExtensions.cs
index 45e41b44d6..7c894dba97 100644
--- a/src/Avalonia.Base/Compatibility/StringCompatibilityExtensions.cs
+++ b/src/Shared/StringCompatibilityExtensions.cs
@@ -3,7 +3,7 @@
 namespace System;
 
 #if !NET6_0_OR_GREATER
-public static class StringCompatibilityExtensions
+internal static class StringCompatibilityExtensions
 {
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static bool Contains(this string str, char search) =>