diff --git a/Directory.Packages.props b/Directory.Packages.props
index 36bf56d..5c98927 100644
--- a/Directory.Packages.props
+++ b/Directory.Packages.props
@@ -9,6 +9,7 @@
     <PackageVersion Include="Microsoft.SourceLink.AzureRepos.Git" Version="8.0.0" />
     <PackageVersion Include="Microsoft.Testing.Extensions.CodeCoverage" Version="18.3.1" />
     <PackageVersion Include="Microsoft.Testing.Extensions.TrxReport" Version="2.0.2" />
+    <PackageVersion Include="Polyfill" Version="9.7.0" />
     <PackageVersion Include="System.Memory" Version="4.5.5" />
   </ItemGroup>
 </Project>
diff --git a/Semantics.Quantities/Semantics.Quantities.csproj b/Semantics.Quantities/Semantics.Quantities.csproj
index f4a7ce5..e8264e9 100644
--- a/Semantics.Quantities/Semantics.Quantities.csproj
+++ b/Semantics.Quantities/Semantics.Quantities.csproj
@@ -5,5 +5,8 @@
   <PropertyGroup>
     <TargetFrameworks>net9.0;net8.0;net7.0;</TargetFrameworks>
   </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Polyfill" />
+  </ItemGroup>
 
 </Project>
diff --git a/Semantics.Strings/Semantics.Strings.csproj b/Semantics.Strings/Semantics.Strings.csproj
index e08e5c4..579ac6f 100644
--- a/Semantics.Strings/Semantics.Strings.csproj
+++ b/Semantics.Strings/Semantics.Strings.csproj
@@ -9,5 +9,8 @@
     <!-- CA2249: Consider using String.Contains instead of String.IndexOf -->
     <!-- IDE0057: Substring can be simplified -->
   </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Polyfill" />
+  </ItemGroup>
 
 </Project>