diff --git a/RegExtract/CompatibilityDefinitions.cs b/RegExtract/CompatibilityDefinitions.cs
deleted file mode 100644
index 358b87e..0000000
--- a/RegExtract/CompatibilityDefinitions.cs
+++ /dev/null
@@ -1,7 +0,0 @@
-using System;
-
-// This is here to enable use of record types in .NET 3.1.
-namespace System.Runtime.CompilerServices
-{
-    internal static class IsExternalInit { }
-}
diff --git a/RegExtract/RegExtract.csproj b/RegExtract/RegExtract.csproj
index b4072ef..bd4e0b0 100644
--- a/RegExtract/RegExtract.csproj
+++ b/RegExtract/RegExtract.csproj
@@ -54,8 +54,7 @@ See more docs at project page: https://github.com/sblom/RegExtract
     <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleToAttribute">
       <_Parameter1>RegExtract.Test</_Parameter1>
     </AssemblyAttribute>
-    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleToAttribute"
-                       Condition="'$(Configuration)' == 'Debug'">
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleToAttribute" Condition="'$(Configuration)' == 'Debug'">
       <_Parameter1>LINQPadQuery</_Parameter1>
     </AssemblyAttribute>
   </ItemGroup>
@@ -77,4 +76,11 @@ See more docs at project page: https://github.com/sblom/RegExtract
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="PolySharp" Version="1.14.1">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+
 </Project>