diff --git a/source/Server.Tests/Server.Tests.csproj b/source/Server.Tests/Server.Tests.csproj
index 6899931..9a837ae 100644
--- a/source/Server.Tests/Server.Tests.csproj
+++ b/source/Server.Tests/Server.Tests.csproj
@@ -11,7 +11,7 @@
   <ItemGroup>
     <PackageReference Include="Assent" Version="1.3.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
-    <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="4.1.0" />
     <PackageReference Include="Octopus.Diagnostics" Version="2.1.2" />