diff --git a/source/Server.Tests/Server.Tests.csproj b/source/Server.Tests/Server.Tests.csproj
index 7b0deca..de6a1c3 100644
--- a/source/Server.Tests/Server.Tests.csproj
+++ b/source/Server.Tests/Server.Tests.csproj
@@ -10,7 +10,7 @@
   <ItemGroup>
     <PackageReference Include="Assent" Version="1.3.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.0.1" />
-    <PackageReference Include="NSubstitute" Version="3.1.0" />
+    <PackageReference Include="NSubstitute" Version="4.4.0" />
     <PackageReference Include="NUnit" Version="3.13.2" />
     <PackageReference Include="NUnit3TestAdapter" Version="4.0.0" />
     <PackageReference Include="Octokit" Version="0.32.0" />