diff --git a/src/Hyperion.Tests/Hyperion.Tests.csproj b/src/Hyperion.Tests/Hyperion.Tests.csproj
index df5fab8..419b8e1 100644
--- a/src/Hyperion.Tests/Hyperion.Tests.csproj
+++ b/src/Hyperion.Tests/Hyperion.Tests.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <Import Project="..\common.props" />
   <Import Project="..\xunitSettings.props" />
 
@@ -72,7 +72,7 @@
   <ItemGroup>
     <PackageReference Include="FluentAssertions" Version="$(FluentAssertionsVersion)" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="$(TestSdkVersion)" />
-    <PackageReference Include="System.Collections.Immutable" Version="5.0.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="9.0.4" />
     <PackageReference Include="System.Security.Principal.Windows" Version="5.0.0" />
     <PackageReference Include="xunit" Version="$(XunitVersion)" />
     <PackageReference Include="xunit.runner.visualstudio" Version="$(XunitRunnerVersion)" />