diff --git a/OpenSkillSharp.Tests/Models/PlackettLuceTests.cs b/OpenSkillSharp.Tests/Models/PlackettLuceTests.cs
index b199fa8..75f4701 100644
--- a/OpenSkillSharp.Tests/Models/PlackettLuceTests.cs
+++ b/OpenSkillSharp.Tests/Models/PlackettLuceTests.cs
@@ -153,7 +153,7 @@ public void Rate_Balance()
     [Fact]
     public void Rate_AllScoresTied()
     {
-        PlackettLuce model = new PlackettLuce { Mu = 30, Sigma = 30.0 / 3 };
+        PlackettLuce model = new() { Mu = 30, Sigma = 30.0 / 3 };
 
         ITeam[] teams = [new Team { Players = [model.Rating()] }, new Team { Players = [model.Rating()] }];
         ITeam[] result = model.Rate(teams, scores: [0, 0]).ToArray();
diff --git a/OpenSkillSharp.Tests/OpenSkillSharp.Tests.csproj b/OpenSkillSharp.Tests/OpenSkillSharp.Tests.csproj
index 9cf55e8..0afd959 100644
--- a/OpenSkillSharp.Tests/OpenSkillSharp.Tests.csproj
+++ b/OpenSkillSharp.Tests/OpenSkillSharp.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>net9.0</TargetFramework>
+        <TargetFramework>net8.0</TargetFramework>
         <ImplicitUsings>enable</ImplicitUsings>
         <Nullable>enable</Nullable>
 
diff --git a/OpenSkillSharp/OpenSkillSharp.csproj b/OpenSkillSharp/OpenSkillSharp.csproj
index 58d2e5a..21e4fb9 100644
--- a/OpenSkillSharp/OpenSkillSharp.csproj
+++ b/OpenSkillSharp/OpenSkillSharp.csproj
@@ -1,7 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>net9.0</TargetFramework>
         <ImplicitUsings>enable</ImplicitUsings>
         <Nullable>enable</Nullable>
         <Title>OpenSkillSharp</Title>
@@ -14,6 +13,7 @@
         <RepositoryType>git</RepositoryType>
         <PackageTags>ranking, rating, elo, trueskill, openskill, bayesian</PackageTags>
         <Copyright>Copyright (c) 2025 Patrick Lacni</Copyright>
+        <TargetFrameworks>net9.0;net8.0</TargetFrameworks>
     </PropertyGroup>
 
     <ItemGroup>
@@ -25,4 +25,10 @@
         <PackageReference Include="MathNet.Numerics" Version="5.0.0"/>
     </ItemGroup>
 
+    <ItemGroup>
+        <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleTo">
+            <_Parameter1>$(MSBuildProjectName).Tests</_Parameter1>
+        </AssemblyAttribute>
+    </ItemGroup>
+
 </Project>
diff --git a/OpenSkillSharp/Util/Polyfills/EnumerablePolyfills.cs b/OpenSkillSharp/Util/Polyfills/EnumerablePolyfills.cs
new file mode 100644
index 0000000..d439b35
--- /dev/null
+++ b/OpenSkillSharp/Util/Polyfills/EnumerablePolyfills.cs
@@ -0,0 +1,25 @@
+#if !NET9_0_OR_GREATER
+// ReSharper disable once CheckNamespace
+namespace System.Linq;
+
+internal static class EnumerablePolyfills
+{
+    /// <summary>Returns an enumerable that incorporates the element's index into a tuple.</summary>
+    /// <typeparam name="TSource">The type of the elements of <paramref name="source" />.</typeparam>
+    /// <param name="source">The source enumerable providing the elements.</param>
+    /// <exception cref="ArgumentNullException"><paramref name="source" /> is <see langword="null" />.</exception>
+    public static IEnumerable<(int Index, TSource Item)> Index<TSource>(this IEnumerable<TSource> source)
+    {
+        ArgumentNullException.ThrowIfNull(source);
+
+        int index = -1;
+
+        foreach (TSource element in source)
+        {
+            index++;
+            yield return (index, element);
+        }
+    }
+}
+
+#endif
\ No newline at end of file